<TABLE> <S> <C>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM
THE ANNUAL REPORT OF AMERICAN CENTURY MUNICIPAL TRUST AND
IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH REPORT.
</LEGEND>
<CIK> 0000746458
<NAME> AMERICAN CENTURY MUNICIPAL TRUST
<SERIES>
<NUMBER> 91
<NAME> LONG-TERM TAX-FREE FUND
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> MAY-31-2000
<PERIOD-END> MAY-31-2000
<INVESTMENTS-AT-COST> 96,726
<INVESTMENTS-AT-VALUE> 96,126
<RECEIVABLES> 2,019
<ASSETS-OTHER> 1,167
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 99,312
<PAYABLE-FOR-SECURITIES> 2,911
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 107
<TOTAL-LIABILITIES> 3,018
<SENIOR-EQUITY> 99
<PAID-IN-CAPITAL-COMMON> 9,745
<SHARES-COMMON-STOCK> 9,931
<SHARES-COMMON-PRIOR> 11,189
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (2,950)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (600)
<NET-ASSETS> 96,294
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 6,208
<OTHER-INCOME> 0
<EXPENSES-NET> 547
<NET-INVESTMENT-INCOME> 5,661
<REALIZED-GAINS-CURRENT> (2,672)
<APPREC-INCREASE-CURRENT> (6,002)
<NET-CHANGE-FROM-OPS> (3,013)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (5,661)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 4,348
<NUMBER-OF-SHARES-REDEEMED> (6,086)
<SHARES-REINVESTED> 447
<NET-CHANGE-IN-ASSETS> (21,290)
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 540
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 547
<AVERAGE-NET-ASSETS> 106,631
<PER-SHARE-NAV-BEGIN> 10.48
<PER-SHARE-NII> 0.52
<PER-SHARE-GAIN-APPREC> (0.78)
<PER-SHARE-DIVIDEND> (0.52)
<PER-SHARE-DISTRIBUTIONS> 0.00
<RETURNS-OF-CAPITAL> 0.00
<PER-SHARE-NAV-END> 9.70
<EXPENSE-RATIO> 0.51
</TABLE>
