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                                MFS SERIES TRUST X
               500 Boylston Street, Boston, Massachusetts  02116-3741
                                Phone 617-954-5000

                                                         May 17, 2005


VIA EDGAR
Securities and Exchange Commission
Judiciary Plaza
450 Fifth Street, NW
Washington, DC 20549


       RE: REQUEST FOR WITHDRAWAL OF POST-EFFECTIVE AMENDMENT NO.55 TO
           REGISTRATION STATEMENT ON FORM N-1A FOR MFS BOND DIVERSIFICATION
           FUND, A SERIES OF TRUST X
           FILE NO. 33-1657, 811-4492; ACCESSION NO. 0001047469-05-006333
           --------------------------------------------------------------

Ladies and Gentlemen:

    Pursuant to Rule 477 under the Securities Act of 1933, the MFS Series
Trust X ("Registrant"), on behalf of MFS Bond Diversification Fund, a series
of the Registrant (the "Fund"), respectfully requests that the Securities and
Exchange Commission (the "Commission") consent to the withdrawal of the above
captioned Post-Effective Amendment No. 55 to the Registration Statement (File
No. 33-1657) filed with the Commission at 13:21 PM on March 14, 2005 (the
"Registration Statement").

    This request for withdrawal is being made because the Fund will not be
launched at this time. The Registration Statement has not yet been declared
effective and no securities were sold in connection with the Registration
Statement.

    Registrant respectfully submits that a withdrawal of the Post-Effective
Amendment No. 55 to the Registration Statement is consistent with the public
interest and the protection of investors in light of the circumstances
described above. Any questions regarding this matter may be directed to Chris
Bohane at 617-954-5822 or the undersigned at 617-954-5047.


                                          Sincerely,

                                          JAMES F. DESMARAIS
                                          James F. Desmarais
                                          Assistant Secretary



   cc:   A. D'Angelo
         E. Reza (Ropes & Gray)