CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002
     -----------------------------------------------------------------------


     In connection with the shareholder report of American Century Municipal
Trust (the "Registrant") on Form N-CSR for the period ending May 31, 2007 (the
"Report"), we, the undersigned, certify, pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002, that:

         (1)   The Report fully complies with the requirements of Section 15(d)
               of the Securities Exchange Act of 1934; and

         (2)   The information contained in the Report fairly presents, in all
               material respects, the financial condition and results of
               operations of the Registrant.


Dated:  July 20, 2007

                                           /s/ Jonathan S. Thomas
                                           -------------------------------------
                                           Jonathan S. Thomas
                                           President
                                           (chief executive officer)


                                           /s/ Robert J. Leach
                                           -------------------------------------
                                           Robert J. Leach
                                           Vice President, Treasurer, and
                                           Chief Financial Officer
                                           (chief financial officer)