SECURITIES AND EXCHANGE ~~COMMISSION Washington~~COMMISSIONWashington, D.C. 20549

FORM 8-~~K CURRENT~~KCURRENT REPORT

Pursuant to Section 13 or 15(d) of ~~the Securities~~theSecurities Exchange Act of 1934

~~July 23, 2004~~ Date of Report (date of earliest event reported) : September 27, 2004

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.

as ~~Depositor~~WAMU ~~and~~MORTGAGE ~~Master~~PASS-THROUGH ~~Servicer~~CERTIFICATES SERIES ~~under a~~2004-AR9 ~~Pooling~~(Exact ~~and~~name ~~Servicing~~of ~~Agreement~~Registrant ~~dated~~ as ofspecified ~~July~~in 1,its ~~2004 providing for the issuance of $849,699,100 (Approximate~~charter)

WaMu MORTGAGE PASS-THROUGH CERTIFICATES SERIES 2004-AR9 (Exact name of Registrant as specified in its charter)

Delaware	333-103345-46	94-2528990
(State or other jurisdiction of incorporation)	(Commission File Number)	(I.R.S. Employer Identification No.)

Delaware		333-103345		94-2528990
(State or other jurisdiction of incorporation)		(Commission File Number)		(I.R.S. Employer Identification No.)

1201 THIRD AVENUE, WMT 1706
SEATTLE, WASHINGTON 98101
(Address of principal executive offices and Zip Code)

Registrant's telephone number, including area code: (206) 377-8555

~~ITEM~~SECTION 78. ~~Financial~~ OTHER ~~Statements and Exhibits.~~EVENTS

~~The~~ITEM ~~following~~8.01 Other ~~exhibit is filed herewith:~~Events

This Current Report on Form 8-K relates to the distribution report furnished to certificate holders in connection with the September 2004 distribution.

~~4.1~~ SECTION ~~Pooling and Servicing Agreement by and among Washington Mutual Mortgage Securities Corp~~9., FINANCIAL asSTATEMENTS ~~Depositor~~AND ~~and Master Servicer, Citibank, N.A., as Trustee, and Christiana Bank & Trust Company, as Delaware Trustee, dated as of July 1, 2004.~~EXHIBITS

~~The~~ITEM ~~Mortgage~~9.01 ~~Loan~~Financial ~~Schedule,~~Statements ~~included as Exhibit D to the Pooling~~ and ~~Servicing Agreement, has been intentionally omitted from this filing. Copies may be obtained from Washington Mutual Mortgage Securities Corp. or Citibank, N.A. by contacting,~~Exhibits

in(a) ~~the~~Not ~~case of Washington Mutual Mortgage Securities Corp.,~~applicable

~~Laura Kelsey Master Servicing Department Washington Mutual Mortgage Securities Corp. 75 N. Fairway Drive,VHF2A01 Vernon Hills, IL 60061 Telephone:~~ (~~847~~b) ~~393-5198~~Not ~~Facsimile: (847) 549-2997~~applicable

~~in the case of Citibank, N.A.,~~(c) Exhibits

Karen Schluter Citibank, N.A. 111 Wall Street 14th Floor, Zone 3 New York, NY 10005 Telephone: (212) 657-7781 Facsimile: (212) 657-4009

Exhibit No.	Description

99.1	WaMu Mortgage Pass-Through Certificates, Series 2004-AR9 Monthly Distribution Report for September 2004

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

	WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.
Date: August 9, 2004	By:	/s/ David H. ZielkeDavid H. Zielke First Vice President and Counsel (Authorized Officer)
Date: September 29, 2004	By:	/s/ Tammy SpriggsTammy SpriggsFirst Vice President (Authorized Officer)

~~Exhibit Index~~3

~~Exhibit~~EXHIBIT No. Description 4.1 Pooling and Servicing Agreement by and among Washington Mutual Mortgage Securities Corp., as Depositor and Master Servicer, Citibank, N.A., as Trustee, and Christiana Bank & Trust Company, as Delaware Trustee, dated as of July 1, 2004. INDEX

Exhibit No.	Description

99.1	WaMu Mortgage Pass-Through Certificates, Series 2004-AR9 Monthly Distribution Report for September 2004

Filing Compare · WaMu Mortgage Pass-Through Certificates, Series 2004-AR9