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

~~March 24, 2005~~ Date of Report (date of earliest event reported) : April 25, 2005

WASHINGTON MUTUAL MORTGAGE SECURITIES CORP.

~~as Depositor and Master~~ ~~Servicer~~WAMU ~~under a Pooling and Servicing Agreement dated as of March 1, 2005 providing for the issuance of WaMu~~ MORTGAGE PASS-THROUGH CERTIFICATES SERIES 2005-AR4 (Exact name of Registrant as specified in its charter)

Delaware	333-103345-60	~~333~~94-~~103345~~2528990	~~94-2528990~~
(State or other jurisdiction of incorporation)		(Commission File Number)	(I.R.S. Employer Identification No.)
(State or other jurisdictionof incorporation)	(Commission File Number)	(I.R.S. EmployerIdentification 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.01 Other ~~filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:~~Events

This Current Report on Form 8-K relates to the distribution report furnished to certificate holders in connection with the April 2005 distribution.

~~o Written communications~~ ~~pursuant~~SECTION to9. FINANCIAL ~~Rule 425~~STATEMENTS ~~under~~AND ~~the Securities Act (17 CFR 230.425)~~EXHIBITS

~~o Soliciting~~ITEM ~~material pursuant~~9.01 toFinancial ~~Rule 14a-12~~Statements ~~under~~and ~~the Exchange Act (17 CFR 240.14a-12)~~Exhibits

~~o Pre-commencement communications pursuant to Rule 14d-2~~(ba) ~~under~~Not ~~the Exchange Act (17 CFR 240.14d-2(b))~~applicable

~~o Pre-commencement communications pursuant to Rule 13e-4~~(cb) ~~under~~Not ~~the Exchange Act (17 CFR 240.13e-4(c))~~applicable

SECTION 9 FINANCIAL STATEMENTS AND EXHIBITS

Item 9.01. Financial Statements and Exhibits.

The following exhibit is filed herewith:

Exhibit No.	Description

99.1	WaMu Mortgage Pass-Through Certificates, Series 2005-AR4 Monthly Distribution Report for April 2005

4.1 Pooling and Servicing Agreement by and among Washington Mutual Mortgage Securities Corp., as Depositor and Master Servicer, Deutsche Bank National Trust Company , as Trustee, and Deutsche Bank Trust Company , as Delaware Trustee, dated as of March 1, 2005.

The Mortgage Loan Schedule, 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 Deutsche Bank National Trust Company by contacting,:

in the case of Washington Mutual Mortgage Securities Corp.,

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 Deutsche Bank National Trust Company,

Alan Sueda Trust Administrator Deutsche Bank National Trust Company 1761 E. St. Andrew Place Santa Ana, CA 92705 Telephone: (714) 247-6315 Facsimile: (714) 247-6329

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: April 7, 2005	By:	/s/ David H. ZielkeDavid H. Zielke First Vice President and Counsel (Authorized Officer)
Date: April 27, 2005	By:	/s/ Tammy SpriggsTammy SpriggsFirst Vice President (Authorized Officer)

~~Exhibit Index~~ 3

~~4.1~~EXHIBIT Pooling and Servicing Agreement by and among Washington Mutual Mortgage Securities Corp., as Depositor and Master Servicer, Deutsche Bank National Trust Company, as Trustee, and Deutsche Bank Trust Company Delaware, as Delaware Trustee, dated as of March 1, 2005.INDEX

Exhibit No.	Description

99.1	WaMu Mortgage Pass-Through Certificates, Series 2005-AR4 Monthly Distribution Report for April 2005

Filing Compare · WaMu Mortgage Pass-Through Certificates, Series 2005-AR4