WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.

<TABLE> <S> <C>

<ARTICLE> 6
<CIK> 0000320282
<NAME> SMITH BARNEY MUNICIPAL MONEY MARKET FUND, INC. CLASS Y
<SERIES>

<S>                             <C>
<PERIOD-TYPE>                   YEAR
<FISCAL-YEAR-END>                          MAR-31-1999
<PERIOD-END>                               MAR-31-1999
<INVESTMENTS-AT-COST>                    7,110,939,917
<INVESTMENTS-AT-VALUE>                   7,110,939,917
<RECEIVABLES>                               51,889,745
<ASSETS-OTHER>                                       0
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<TOTAL-ASSETS>                           7,163,699,612
<PAYABLE-FOR-SECURITIES>                    23,606,645
<SENIOR-LONG-TERM-DEBT>                              0
<OTHER-ITEMS-LIABILITIES>                   11,986,382
<TOTAL-LIABILITIES>                         35,593,027
<SENIOR-EQUITY>                                      0
<PAID-IN-CAPITAL-COMMON>                 7,057,401,607
<SHARES-COMMON-STOCK>                       23,991,378
<SHARES-COMMON-PRIOR>                          489,251
<ACCUMULATED-NII-CURRENT>                            0
<OVERDISTRIBUTION-NII>                               0
<ACCUMULATED-NET-GAINS>                      (578,281)
<OVERDISTRIBUTION-GAINS>                             0
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<DIVIDEND-INCOME>                                    0
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<OTHER-INCOME>                                       0
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<NET-INVESTMENT-INCOME>                    188,051,702
<REALIZED-GAINS-CURRENT>                       469,190
<APPREC-INCREASE-CURRENT>                            0
<NET-CHANGE-FROM-OPS>                      188,520,892
<EQUALIZATION>                                       0
<DISTRIBUTIONS-OF-INCOME>                      632,914
<DISTRIBUTIONS-OF-GAINS>                             0
<DISTRIBUTIONS-OTHER>                                0
<NUMBER-OF-SHARES-SOLD>                    120,903,944
<NUMBER-OF-SHARES-REDEEMED>                 97,709,608
<SHARES-REINVESTED>                            307,791
<NET-CHANGE-IN-ASSETS>                     790,913,920
<ACCUMULATED-NII-PRIOR>                              0
<ACCUMULATED-GAINS-PRIOR>                            0
<OVERDISTRIB-NII-PRIOR>                              0
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<GROSS-ADVISORY-FEES>                       32,200,646
<INTEREST-EXPENSE>                                   0
<GROSS-EXPENSE>                             42,082,398
<AVERAGE-NET-ASSETS>                        13,099,767
<PER-SHARE-NAV-BEGIN>                            1.000
<PER-SHARE-NII>                                  0.029
<PER-SHARE-GAIN-APPREC>                              0
<PER-SHARE-DIVIDEND>                             0.029
<PER-SHARE-DISTRIBUTIONS>                            0
<RETURNS-OF-CAPITAL>                                 0
<PER-SHARE-NAV-END>                              1.000
<EXPENSE-RATIO>                                  0.620
[AVG-DEBT-OUTSTANDING]                               0
[AVG-DEBT-PER-SHARE]                                 0


</TABLE>