MFS® INVESTMENT MANAGEMENT

500 BOYLSTON STREET, BOSTON, MASSACHUSETTS  02116-3741

(617) 954-5000

June 1, 2010

VIA EDGAR

United States Securities & Exchange Commission

100 F Street, N.E.

Washington, DC  20549

Re: MFSÒ Series Trust III (the “Trust”) (File No. 333158507) on Behalf of MFSÒHigh Income Fund, MFSÒ High Yield Opportunities Fund and MFSÒ Municipal High Income Fund (the “Funds”)

Ladies and Gentlemen:

Pursuant to Rule 497(j) under the Securities Act of 1933, as amended, please accept this letter on behalf of the Trust as certification that the Prospectuses and Statements of Additional Information for the Funds do not differ from those contained in Post-Effective Amendment No. 45, (the "Amendment") to the Trust's Registration Statement on Form N-1A.  The Amendment was filed electronically on May 27, 2010.

Please call the undersigned at (617) 954-5064 or Keli Davis at (617) 954- 5873 with any questions you may have.

Very truly yours,

TIMOTHY M. FAGAN

Timothy M. Fagan

Vice President & Senior Counsel

TMF/bjn