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

~~August 24, 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 aPooling and Servicing Agreement~~ 2004-CB3 ~~dated~~(Exact asname of ~~August~~Registrant 1,as ~~2004~~specified ~~providing~~in ~~for~~its ~~the issuance of $301,582,806 (Approximate~~charter)

WaMu MORTGAGE PASS-THROUGH CERTIFICATES SERIES 2004-CB3(Exact name of Registrant as specified in its charter)

Delaware	333-103345-49	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

~~(Former~~SECTION ~~name~~8. OTHER ~~or former address, if changed since last report)~~EVENTS

~~Check~~ITEM ~~the appropriate box below if the Form~~ 8~~-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A~~.2.01 Other ~~below):~~ Events

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

~~o Written~~ ~~communications~~SECTION ~~pursuant~~9. FINANCIAL toSTATEMENTS ~~Rule 425~~AND ~~under the Securities Act (17 CFR 230.425)~~ EXHIBITS

o Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

SECTION 9 - FINANCIAL STATEMENTS AND EXHIBITS

ITEM 9.01 Financial Statements and Exhibits

~~The~~(a) ~~following~~Not ~~exhibit is filed herewith:~~applicable

~~4.1~~(b) ~~Pooling~~Not 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 August 1, 2004.applicable

The definition of Class C-Y Principal Reduction Amounts , included as Appendix 1 to the Pooling and Servicing Agreement, and the Mortgage Loan Schedule, included as Exhibit D to the Pooling and Servicing Agreement, have been intentionally omitted from this filing. Copies may be obtained from Washington Mutual Mortgage Securities Corp. or Citibank, N.A. by contacting:(c) Exhibits

in the case of Washington Mutual Mortgage Securities Corp.,

Exhibit No.	Description

99.1	WaMu Mortgage Pass-Through Certificates, Series 2004-CB3 Monthly Distribution Report for September 2004

Laura Kelsey Master Servicing Department Washington Mutual Mortgage Securities Corp. 75 N. Fairway Drive,VHF2A01 Vernon Hills, IL 60061 Telephone: (847) 393-5198 Facsimile: (847) 549-2997

in the case of Citibank, N.A.,

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

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: September 8, 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~~EXHIBIT ~~Index~~INDEX

Exhibit No. Description 499.1 ~~Pooling~~WaMu ~~and Servicing Agreement by and among Washington Mutual~~ Mortgage ~~Securities~~ ~~Corp.,~~Pass-Through ~~as Depositor and Master Servicer~~Certificates, ~~Citibank,~~Series ~~N.A., as Trustee,~~2004-CB3 ~~and~~Monthly ~~Christiana~~Distribution ~~Bank~~Report &for ~~Bank~~September ~~Trust Company, as Delaware Trustee, dated as of August 1,~~ 2004.

Filing Compare · WaMu Mortgage Pass-Through Certificates, Series 2004-CB3