WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.03AR12
Distribution Date: 09/27/2004

Class	Cusip	Orig Prin Bal	Begin Prin Bal	Int Rate Accrued	Int Rate Paid	Int Dist	Prin Dist	Int Shortfall	PPIS	Uncomp Int Shortfall	Prin Loss	Deferred Interest	Int Reimbursed	Unsched Int	Prin Reimbursed	Subsequent Recoveries	Total Dist	Ending Class Bal
A1	92922FKP2	$148,732,000.00	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
A2	92922FKQ0	$67,785,000.00	$52,927,165.78	2.4460000000%	2.4460000000%	$107,883.21	$7,164,220.84	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$7,272,104.05	$45,762,944.94
A3	92922FKR8	$102,740,000.00	$102,740,000.00	3.3560000000%	3.3560000000%	$287,329.53	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$287,329.53	$102,740,000.00
A4	92922FKS6	$72,991,000.00	$72,991,000.00	3.7430000000%	3.7430000000%	$227,671.09	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$227,671.09	$72,991,000.00
A5	92922FKT4	$70,827,000.00	$70,827,000.00	4.0430000000%	4.0430000000%	$238,627.97	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$238,627.97	$70,827,000.00
A6	92922FKU1	$141,623,000.00	$141,623,000.00	3.9610000000%	3.9610000000%	$467,473.92	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$467,473.92	$141,623,000.00
X	92922FKW7	$604,698,000.00	$441,108,165.78	0.5237651397%	0.5237651397%	$192,530.90	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$192,530.90	$433,943,944.94
B1	92922FKX5	$7,492,000.00	$7,483,812.64	4.5667651397%	4.5667651397%	$28,480.68	$1,120.94	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$29,601.62	$7,482,691.70
B2	92922FKY3	$4,994,000.00	$4,988,542.49	4.5667651397%	4.5667651397%	$18,984.58	$747.19	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$19,731.78	$4,987,795.30
B3	92922FKZ0	$3,121,000.00	$3,117,589.33	4.5667651397%	4.5667651397%	$11,864.42	$466.96	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$12,331.37	$3,117,122.37
B4	92922FLA4	$1,248,000.00	$1,246,636.17	4.5667651397%	4.5667651397%	$4,744.25	$186.72	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$4,930.97	$1,246,449.45
B5	92922FLB2	$936,000.00	$934,977.12	4.5667651397%	4.5667651397%	$3,558.18	$140.04	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$3,698.23	$934,837.08
B6	92922FLC0	$1,877,207.97	$1,875,156.54	4.5667651397%	4.5667651397%	$7,136.17	$280.87	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$7,417.03	$1,874,875.67
SFEE	XXXXXXXXX	$533,871,000.00	$370,281,165.78	0.5093898021%	0.5093898021%	$157,181.21	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$157,181.21	$363,116,944.94
R	92922FKV9	$100.00	$0.00	0.0000000000%	0.0000000000%	$0.29	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.29	$0.00
R_SYN	XXXXXXXXX	$0.00	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
Total		$624,366,307.97	$460,754,880.07			$1,753,466.39	$7,167,163.57	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$8,920,629.96	$453,587,716.50

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.03AR12
Distribution Date: 09/27/2004

Class	Orig Face	Beg Bal	Prin Loss	Prin Reimbursed	Subsequent Recoveries	Deferred Interest	Total Prin	End Cert Pct	End Cert Bal
A1	$148,732,000.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	0.0000000000	$0.00
A2	$67,785,000.00	$52,927,165.78	$0.00	$0.00	$0.00	$0.00	$7,164,220.84	0.6751190520	$45,762,944.94
A3	$102,740,000.00	$102,740,000.00	$0.00	$0.00	$0.00	$0.00	$0.00	1.0000000000	$102,740,000.00
A4	$72,991,000.00	$72,991,000.00	$0.00	$0.00	$0.00	$0.00	$0.00	1.0000000000	$72,991,000.00
A5	$70,827,000.00	$70,827,000.00	$0.00	$0.00	$0.00	$0.00	$0.00	1.0000000000	$70,827,000.00
A6	$141,623,000.00	$141,623,000.00	$0.00	$0.00	$0.00	$0.00	$0.00	1.0000000000	$141,623,000.00
X	$604,698,000.00	$441,108,165.78	$0.00	$0.00	$0.00	$0.00	$0.00	0.7176209363	$433,943,944.94
B1	$7,492,000.00	$7,483,812.64	$0.00	$0.00	$0.00	$0.00	$1,120.94	0.9987575681	$7,482,691.70
B2	$4,994,000.00	$4,988,542.49	$0.00	$0.00	$0.00	$0.00	$747.19	0.9987575691	$4,987,795.30
B3	$3,121,000.00	$3,117,589.33	$0.00	$0.00	$0.00	$0.00	$466.96	0.9987575681	$3,117,122.37
B4	$1,248,000.00	$1,246,636.17	$0.00	$0.00	$0.00	$0.00	$186.72	0.9987575721	$1,246,449.45
B5	$936,000.00	$934,977.12	$0.00	$0.00	$0.00	$0.00	$140.04	0.9987575641	$934,837.08
B6	$1,877,207.97	$1,875,156.54	$0.00	$0.00	$0.00	$0.00	$280.87	0.9987575697	$1,874,875.67
SFEE	$533,871,000.00	$370,281,165.78	$0.00	$0.00	$0.00	$0.00	$0.00	0.6801585869	$363,116,944.94
R	$100.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	0.0000000000	$0.00
R_SYN	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	0.0000000000	$0.00
Total	$624,366,307.97	$460,754,880.07	$0.00	$0.00	$0.00	$0.00	$7,167,163.57	0.7264769266	$453,587,716.50

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.03AR12
Distribution Date: 09/27/2004
PER $1000 DENOMINATION
Class	Orig Face	Beg Bal	Prin Loss	Prin Reimbursed	Subsequent Recoveries	Deferred Interest	Total Prin	End Cert Pct	End Cert Bal
A1	$148,732,000.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
A2	$67,785,000.00	780.80940887	0.00000000	0.00000000	0.00000000	0.00000000	105.69035686	0.6751190520	675.11905200
A3	$102,740,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.0000000000	1,000.00000000
A4	$72,991,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.0000000000	1,000.00000000
A5	$70,827,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.0000000000	1,000.00000000
A6	$141,623,000.00	1,000.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.0000000000	1,000.00000000
X	$604,698,000.00	729.46853765	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.7176209363	717.62093630
B1	$7,492,000.00	998.90718633	0.00000000	0.00000000	0.00000000	0.00000000	0.14961826	0.9987575681	998.75756807
B2	$4,994,000.00	998.90718662	0.00000000	0.00000000	0.00000000	0.00000000	0.14961754	0.9987575691	998.75756908
B3	$3,121,000.00	998.90718680	0.00000000	0.00000000	0.00000000	0.00000000	0.14961871	0.9987575681	998.75756809
B4	$1,248,000.00	998.90718750	0.00000000	0.00000000	0.00000000	0.00000000	0.14961538	0.9987575721	998.75757212
B5	$936,000.00	998.90717949	0.00000000	0.00000000	0.00000000	0.00000000	0.14961538	0.9987575641	998.75756410
B6	$1,877,207.97	998.90719087	0.00000000	0.00000000	0.00000000	0.00000000	0.14962114	0.9987575697	998.75756973
SFEE	$533,871,000.00	693.57797254	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.6801585869	680.15858689
R	$100.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000
R_SYN	$0.00	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.0000000000	0.00000000

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.03AR12
Distribution Date: 09/27/2004

Class	Orig Face	Int Rate Accrued	Int Rate Paid	Beg Cert Prin/Not Bal	Current Int Accrued	Int Shortfall	PPIS	Uncompensated Int Shortfall	Unscheduled Int	Int Reimbursed	Total Int Dist
A1	$148,732,000.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
A2	$67,785,000.00	2.4460000000%	2.4460000000%	$52,927,165.78	$107,883.21	$0.00	$0.00	$0.00	$0.00	$0.00	$107,883.21
A3	$102,740,000.00	3.3560000000%	3.3560000000%	$102,740,000.00	$287,329.53	$0.00	$0.00	$0.00	$0.00	$0.00	$287,329.53
A4	$72,991,000.00	3.7430000000%	3.7430000000%	$72,991,000.00	$227,671.09	$0.00	$0.00	$0.00	$0.00	$0.00	$227,671.09
A5	$70,827,000.00	4.0430000000%	4.0430000000%	$70,827,000.00	$238,627.97	$0.00	$0.00	$0.00	$0.00	$0.00	$238,627.97
A6	$141,623,000.00	3.9610000000%	3.9610000000%	$141,623,000.00	$467,473.92	$0.00	$0.00	$0.00	$0.00	$0.00	$467,473.92
X	$604,698,000.00	0.5237651397%	0.5237651397%	$441,108,165.78	$192,530.90	$0.00	$0.00	$0.00	$0.00	$0.00	$192,530.90
B1	$7,492,000.00	4.5667651397%	4.5667651397%	$7,483,812.64	$28,480.68	$0.00	$0.00	$0.00	$0.00	$0.00	$28,480.68
B2	$4,994,000.00	4.5667651397%	4.5667651397%	$4,988,542.49	$18,984.58	$0.00	$0.00	$0.00	$0.00	$0.00	$18,984.58
B3	$3,121,000.00	4.5667651397%	4.5667651397%	$3,117,589.33	$11,864.42	$0.00	$0.00	$0.00	$0.00	$0.00	$11,864.42
B4	$1,248,000.00	4.5667651397%	4.5667651397%	$1,246,636.17	$4,744.25	$0.00	$0.00	$0.00	$0.00	$0.00	$4,744.25
B5	$936,000.00	4.5667651397%	4.5667651397%	$934,977.12	$3,558.18	$0.00	$0.00	$0.00	$0.00	$0.00	$3,558.18
B6	$1,877,207.97	4.5667651397%	4.5667651397%	$1,875,156.54	$7,136.17	$0.00	$0.00	$0.00	$0.00	$0.00	$7,136.17
SFEE	$533,871,000.00	0.5093898021%	0.5093898021%	$370,281,165.78	$157,181.21	$0.00	$0.00	$0.00	$0.00	$0.00	$157,181.21
R	$100.00	0.0000000000%	0.0000000000%	$0.00	$0.29	$0.00	$0.00	$0.00	$0.00	$0.00	$0.29
R_SYN	$0.00	0.0000000000%	0.0000000000%	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
Total	$624,366,307.97			$460,754,880.07	$1,753,466.39	$0.00	$0.00	$0.00	$0.00	$0.00	$1,753,466.39

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.03AR12
Distribution Date: 09/27/2004
PER $1000 DENOMINATION
Class	Orig Face	Int Rate Accrued	Int Rate Paid	Beg Cert Prin/Not Bal	Curent Int Accrued	Int Shortfall	PPIS	Uncompensated Int Shortfall	Unscheduled Int	Int Reimbursed	Total Int Dist
A1	$148,732,000.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000
A2	$67,785,000.00	2.4460000000%	2.4460000000%	780.80940887	1.59154990	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	1.59154990
A3	$102,740,000.00	3.3560000000%	3.3560000000%	1,000.00000000	2.79666663	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.79666663
A4	$72,991,000.00	3.7430000000%	3.7430000000%	1,000.00000000	3.11916661	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.11916661
A5	$70,827,000.00	4.0430000000%	4.0430000000%	1,000.00000000	3.36916670	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.36916670
A6	$141,623,000.00	3.9610000000%	3.9610000000%	1,000.00000000	3.30083334	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.30083334
X	$604,698,000.00	0.5237651397%	0.5237651397%	729.46853765	0.31839183	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.31839183
B1	$7,492,000.00	4.5667651397%	4.5667651397%	998.90718633	3.80147891	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.80147891
B2	$4,994,000.00	4.5667651397%	4.5667651397%	998.90718662	3.80147777	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.80147777
B3	$3,121,000.00	4.5667651397%	4.5667651397%	998.90718680	3.80148029	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.80148029
B4	$1,248,000.00	4.5667651397%	4.5667651397%	998.90718750	3.80148237	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.80148237
B5	$936,000.00	4.5667651397%	4.5667651397%	998.90717949	3.80147436	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.80147436
B6	$1,877,207.97	4.5667651397%	4.5667651397%	998.90719087	3.80148077	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	3.80148077
SFEE	$533,871,000.00	0.5093898021%	0.5093898021%	693.57797254	0.29441796	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.29441796
R	$100.00	0.0000000000%	0.0000000000%	0.00000000	2.90000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	2.90000000
R_SYN	$0.00	0.0000000000%	0.0000000000%	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000	0.00000000

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
MASTER SERVICING
MORTGAGE PASS-THROUGH CERTIFICATES
09/2004 DISTRIBUTION REPORT
SERIES: WAMU 03AR12
WEIGHTED AVERAGE PC RATE: 4.56677%
WEIGHTED AVERAGE MATURITY: 350.66893
WEIGHTED AVERAGE LOAN AGE: 9.47733
POOL NUMBER: 2301
ISSUE DATE: 12/22/2003
CERTIFICATE BALANCE AT ISSUE: $624,366,307.97
	TOTAL NUMBER OF MORTAGES	CERTIFICATE ACCOUNT ACTIVITY (@ PCRATE)	CERTIFICATE BALANCE OUTSTANDING
BALANCES FROM LAST FISCAL MONTH-END:	783		$460,754,880.09
PRINCIPAL POOL COLLECTION(S):
Scheduled Principal Collection Due Current Month		$69,012.88
Unscheduled Principal Collection/Reversals		$756,531.44
Liquidations-in-full	11	$6,341,619.25
Subsequent Recoveries		$0.00
Net principal Distributed		$7,167,163.57	-$7,167,163.57

CAPITAL LOSS (PRINCIPAL WRITTEN OFF):			$0.00

BALANCE CURRENT FISCAL MONTH-END:	772		$453,587,716.52

SCHEDULED INTEREST AT MORTGAGE RATE:		$1,916,650.32

UNSCHEDULED INTEREST AT MORTGAGE RATE:
Unscheduled Interest Collection/Reversals		$0.00
Interest Uncollected on Liquidation		$0.00
Interest Uncollected on Non-Earning Assets		$0.00
Interest Uncollected on Prepayment		$0.00
Uncompensated Uncollected Interest		$0.00
Net Unscheduled Interest Distributed		$0.00

OTHER:
Loan Conversion Fees		$0.00
Expense Reimbursements		$0.00
Gain on Liquidations		$0.00
Hazard Insurance Premium Refunds		$0.00
Recoveries Carried Forward		$0.00
Net Other Distributions		$0.00

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
MASTER SERVICING
MORTGAGE PASS-THROUGH CERTIFICATES
09/2004 DISTRIBUTION REPORT
	TOTAL NUMBER OF MORTAGES	CERTIFICATE ACCOUNT ACTIVITY (@ PCRATE)	CERTIFICATE BALANCE OUTSTANDING
SCHEDULED SERVICING FEE EXPENSES:		$163,183.93

UNSCHEDULED SERVICING FEES:
Unscheduled Service Fee Collections/Reversals		$0.00
Servicing Fees Uncollected on Liquidation		$0.00
Servicing Fees Uncollected/Non-Earning Assets		$0.00
Net Unscheduled Service Fees Distributed		$0.00

MISCELLANEOUS EXPENSES:		$0.00

NET FUNDS DISTRIBUTED:		$8,920,629.96

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
MASTER SERVICING
MORTGAGE PASS-THROUGH CERTIFICATES
09/2004 DISTRIBUTION REPORT
SERIES: WAMU 03AR12
WEIGHTED AVERAGE PC RATE: 4.56677%
WEIGHTED AVERAGE MATURITY: 350.66893
WEIGHTED AVERAGE LOAN AGE: 9.47733
POOL NUMBER: ALL
ISSUE DATE: 12/22/2003
CERTIFICATE BALANCE AT ISSUE: $624,366,307.97
	TOTAL NUMBER OF MORTAGES	CERTIFICATE ACCOUNT ACTIVITY (@ PCRATE)	CERTIFICATE BALANCE OUTSTANDING
BALANCES FROM LAST FISCAL MONTH-END:	783		$460,754,880.09
PRINCIPAL POOL COLLECTION(S):
Scheduled Principal Collection Due Current Month		$69,012.88
Unscheduled Principal Collection/Reversals		$756,531.44
Liquidations-in-full	11	$6,341,619.25
Subsequent Recoveries		$0.00
Net principal Distributed		$7,167,163.57	-$7,167,163.57

CAPITAL LOSS (PRINCIPAL WRITTEN OFF):			$0.00

BALANCE CURRENT FISCAL MONTH-END:	772		$453,587,716.52

SCHEDULED INTEREST AT MORTGAGE RATE:		$1,916,650.32

UNSCHEDULED INTEREST AT MORTGAGE RATE:
Unscheduled Interest Collection/Reversals		$0.00
Interest Uncollected on Liquidation		$0.00
Interest Uncollected on Non-Earning Assets		$0.00
Interest Uncollected on Prepayment		$0.00
Uncompensated Uncollected Interest		$0.00
Net Unscheduled Interest Distributed		$0.00

OTHER:
Loan Conversion Fees		$0.00
Expense Reimbursements		$0.00
Gain on Liquidations		$0.00
Hazard Insurance Premium Refunds		$0.00
Recoveries Carried Forward		$0.00
Net Other Distributions		$0.00

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
MASTER SERVICING
MORTGAGE PASS-THROUGH CERTIFICATES
09/2004 DISTRIBUTION REPORT
	TOTAL NUMBER OF MORTAGES	CERTIFICATE ACCOUNT ACTIVITY (@ PCRATE)	CERTIFICATE BALANCE OUTSTANDING
SCHEDULED SERVICING FEE EXPENSES:		$163,183.93

UNSCHEDULED SERVICING FEES:
Unscheduled Service Fee Collections/Reversals		$0.00
Servicing Fees Uncollected on Liquidation		$0.00
Servicing Fees Uncollected/Non-Earning Assets		$0.00
Net Unscheduled Service Fees Distributed		$0.00

MISCELLANEOUS EXPENSES:		$0.00

NET FUNDS DISTRIBUTED:		$8,920,629.96

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.03AR12
Distribution Date: 09/27/2004

Distribution by Group
Pool ID		Principal		Interest		Total
Pool - 2301		$7,167,163.57		$1,753,466.39		$8,920,629.96
Aggregate		$7,167,163.57		$1,753,466.39		$8,920,629.96

Number of Loans and Aggregate Principal Balance By Group
Pool ID	Beg Bal	Beg Count	Paid Off / Liq Count	Rem Count	Sched Prin End Bal	Sched Prin	Prin PrePay / Liq	Unsched Prin / Rev	Total Prin
Pool - 2301	$460,754,880.09	783	11	772	$453,587,716.52	$69,012.88	$6,341,619.25	$756,531.44	$7,167,163.57
Aggregate	$460,754,880.09	783	11	772	$453,587,716.52	$69,012.88	$6,341,619.25	$756,531.44	$7,167,163.57

Delinquency Information by Group
Pool ID	1 Month Count	Sched End Balance	2 Months Count	Sched End Balance	3 Months Count	Sched End Balance	4 Months Count	Sched End Balance
Pool - 2301	8	$4,107,013.25	0	$0.00	0	$0.00	0	$0.00
Aggregate	8	$4,107,013.25	0	$0.00	0	$0.00	0	$0.00

Foreclosure and REO Information by Group
Pool ID		Foreclosure Count		Sched End Balance		REO Count		Sched End Balance
Pool - 2301		0		$0.00		0		$0.00
Aggregate		0		$0.00		0		$0.00

Aggregate Loss Amounts by Group
Pool ID			Count			Loss Amount
Pool - 2301			0			$0.00
Aggregate			0			$0.00

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.03AR12
Distribution Date: 09/27/2004

INSURANCE RESERVES - Group 1
Insurance Type	Original Balance	Claims In Progress	Claims Paid	Coverage Adjustments	Coverage Remaining
MPI	$0.00	$0.00	$0.00	$0.00	$0.00
Special Hazard	$11,836,800.00	$0.00	$0.00	$0.00	$11,836,800.00
Bankruptcy Bond
Single-Units	$100,000.00	$0.00	$0.00	$0.00	$100,000.00
Multi-Units	$0.00	$0.00	$0.00	$0.00	$0.00
Mortgage Repurchase	$12,487,326.14	$0.00	$0.00	$0.00	$12,487,326.14

INSURANCE RESERVES - Aggregate
Insurance Type	Original Balance	Claims In Progress	Claims Paid	Coverage Adjustments	Coverage Remaining
MPI	$0.00	$0.00	$0.00	$0.00	$0.00
Special Hazard	$11,836,800.00	$0.00	$0.00	$0.00	$11,836,800.00
Bankruptcy Bond
Single-Units	$100,000.00	$0.00	$0.00	$0.00	$100,000.00
Multi-Units	$0.00	$0.00	$0.00	$0.00	$0.00
Mortgage Repurchase	$12,487,326.14	$0.00	$0.00	$0.00	$12,487,326.14

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Series: WAMU.03AR12
Distribution Date: 09/27/2004

The Subordinate Certificates provide, to the limited extent described in the Prospectus Supplement, credit support, as well as special hazard, bankruptcy, and fraud coverage to certain Certificates. The "Prospectus Supplement" is that certain Prospectus Supplement, dated December 18,2003 to that certain Prospectus Supplement, dated September 19,2003, to which certain certificates were offered. The special hazard, bankruptcy, and Fraud coverage (collectively, "Credit Enhancements") provided by the Subordinate certificates provide coverage to the Loans, subject to the conditions and limitations to payment specified thereunder.



The Class Principal Balances of each Class of the Class B1,B2,B3,B4,B5,B6 Certificatesimmediately after the principal and interest distribution on 200409 are as follows:

Class			Class Principal Balance
B1			$7,482,691.70
B2			$4,987,795.30
B3			$3,117,122.37
B4			$1,246,449.45
B5			$934,837.08
B6			$1,874,875.67
Total			$19,643,771.56
Capitalized items used but not defined herein have the meanings ascribed to them in the Prospectus Supplement.
The amount of the special hazard coverage, bankruptcy coverage, and fraud coverage, as of the above referenced distribution date, is $11,836,800.00, $100,000.00, $12,487,326.14 respectively, and such coverages are referred to in the table above under the column "Insurance Type" as "special hazard," "bankruptcy bond," and "mortgage repurchase," respectively. However, no policy of insurance exists for any such coverage, notwithstanding the reference to "insurance."

WAMU MORTGAGE PASS THR CERTS SER 2003-AR12 8-K