MFS® SERIES TRUST V

MFS® SERIES TRUST XI

500 Boylston Street, Boston, Massachusetts  02116-3741

617-954-5000

January 20, 2010

VIA EDGAR (as Correspondence)

United States Securities and Exchange Commission

100 F Street, N.E.

Washington, D.C.  20549

Re: Post-Effective Amendment No. 64 to Registration Statement on Form N-1A for MFS Series Trust V (File Nos. 2-38613 and 811-2031) ("Trust V") and Post-Effective Amendment No. 29 to Registration Statement on Form N-1A for MFS Series Trust XI (File Nos. 33-68310 and 811-7992) ("Trust XI")

Ladies and Gentlemen:

As requested, in connection with the filing of the above-referenced Registration Statements, we acknowledge the following:

(i)   the comment process with the SEC or its staff, acting pursuant to delegated authority, does not foreclose the SEC from taking any action with respect to the filing;

(ii)   the comment process with the SEC or its staff, acting pursuant to delegated authority, does not relieve the Trust from their full responsibility for the adequacy and accuracy of the disclosure in the filing; and

(iii)   the Trust may not assert the comment process with the SEC or its staff in connection with the preliminary filing as a defense in any proceeding initiated by the SEC or any person under the federal securities laws of the United States.

The Trust notes that, as indicated in the SEC’s June 24, 2004 release regarding the public release of comment letters and responses, you are requesting such acknowledgements from all companies whose filings are being reviewed.

If you have any questions, please call the undersigned at 617-954-4340.

Very truly yours,

MFS SERIES TRUST V

MFS SERIES TRUST XI

SUSAN A. PEREIRA

Susan A. Pereira

Assistant Secretary