Fitch Rates Washington Mutual MSC $286.7MM Mtge P-T Ctfs Series 2005-RA1.

NEW YORK -- Washington Mutual Mortgage Securities Corp.'s $286,711,000 mortgage pass-through certificates, series 2005-RA1, classes 1-A, 2-A, 3-A, and R (senior certificates) are rated 'AAA' by Fitch. The classes L-B-1 through L-B-6 and 3-B-1 through 3-B-6 certificates are not rated by Fitch.

The 'AAA' rating on the classes 1-A and 2-A certificates reflect the 4.50% subordination provided by the class L-B certificates (which are not rated by Fitch) and the 'AAA' rating on the class 3-A certificates reflects the 3.00% subordination provided by the class 3-B certificates (which are not rated by Fitch). Fitch believes the above credit enhancement will be adequate to support mortgagor defaults as well as bankruptcy, fraud and special hazard losses in limited amounts. The ratings also reflect the quality of the mortgage collateral, the capabilities of Washington Mutual Mortgage Securities Corp. (WMMSC) as master servicer (rated 'RMS2+' by Fitch), and Fitch's confidence in the integrity of the legal and financial structure of the transaction.

The mortgage loans deposited into the Washington Mutual MSC Mortgage Pass-Through Certificates Series 2005-RA1 Trust were purchased by Washington Mutual Mortgage Securities Corp. directly or indirectly from affiliated or unaffiliated third parties who either originated the applicable mortgage loans or purchased the mortgage loans through correspondent or broker channels.

The assets of the trust will consist of three groups of 15- and 30-year fixed-rate loans and hybrid ARMs, secured by first liens on one- to four-family properties. As of the cutoff date (April 1, 2005), the total original principal balance is $297,398,798. Groups 1 and 2 are cross-collateralized and Group 3 is standalone.

The Groups 1 and 2 loans consist of 669 conventional, fully amortizing, 15- and 30-year fixed-rate mortgage loans with an aggregate original principal balance of $117,670,372. The average unpaid principal balance is $175,890. The weighted average loan-to-value ratio (LTV) is 49.4%. Rate/Term and Cash-out refinance loans represent 31.0% and 24.4% of the loan pool, respectively. Second home and investor-occupied loans comprise 6.8% and 8.0% of the group, respectively. The weighted average FICO credit score for the group is 654. The weighted average remaining term for the group is 270 months. The states that represent the largest portion of the mortgage loans are California (22.4%), Florida (11.3%), New York (8.8%), and Texas (8.1%). All other states represent less than 5% of the outstanding balance of the pool.

The Group 3 loans consist of 342 conventional, fully amortizing, 30-year hybrid ARM mortgage loans with an aggregate original principal balance of $179,728,427. The average unpaid principal balance is $525,522. The weighted average LTV is 61.4%. Rate/Term and Cash-out refinance loans represent 34.9% and 38.2% of the loan pool, respectively. Second-home loans comprise 7.8% of the group. The weighted average FICO credit score for the group is 740. The weighted average remaining term for the group is 318 months. The states that represent the largest portion of the mortgage loans are California (49.1%), Massachusetts (6.1%), Washington (5.6%), Florida (5.3%), and Connecticut (5.0%). All other states represent less than 5% of the outstanding balance of the pool.

None of the mortgage loans are 'high cost' loans as defined under any local, state or federal laws. For additional information on Fitch's rating criteria regarding predatory lending legislation, please see the press release issued May 1, 2003 entitled 'Fitch Revises Rating Criteria in Wake of Predatory Lending Legislation,' available on the Fitch Ratings web site at 'www.fitchratings.com'.

The certificates are issued pursuant to a pooling and servicing agreement dated April 1, 2005 among Washington Mutual Mortgage Securities Corp., as depositor and master servicer, and U.S. Bank National Associate, as trustee. For federal income tax purposes, elections will be made to treat the trust as two separate real estate mortgage investment conduits (REMICs).