[ARTICLE] 6
[CIK] 0000320282
[NAME] SMITH BARNEY MUNICIPAL MONEY MARKET FUND, INC. CLASS Y
<TABLE>
<S>                             <C>
[PERIOD-TYPE]                   6-MOS
[FISCAL-YEAR-END]                          MAR-31-1999
[PERIOD-END]                               SEP-30-1998
[INVESTMENTS-AT-COST]                    6,443,710,348
[INVESTMENTS-AT-VALUE]                   6,443,710,348
[RECEIVABLES]                               85,490,000
[ASSETS-OTHER]                              40,642,668
[OTHER-ITEMS-ASSETS]                           550,798
[TOTAL-ASSETS]                           6,570,393,814
[PAYABLE-FOR-SECURITIES]                    94,288,890
[SENIOR-LONG-TERM-DEBT]                              0
[OTHER-ITEMS-LIABILITIES]                   12,561,133
[TOTAL-LIABILITIES]                        106,850,023
[SENIOR-EQUITY]                                      0
[PAID-IN-CAPITAL-COMMON]                 6,458,074,943
[SHARES-COMMON-STOCK]                          200,632
[SHARES-COMMON-PRIOR]                          489,251
[ACCUMULATED-NII-CURRENT]                            0
[OVERDISTRIBUTION-NII]                               0
[ACCUMULATED-NET-GAINS]                         51,861
[OVERDISTRIBUTION-GAINS]                             0
[ACCUM-APPREC-OR-DEPREC]                             0
[NET-ASSETS]                             6,463,543,791
[DIVIDEND-INCOME]                                    0
[INTEREST-INCOME]                          118,167,114
[OTHER-INCOME]                                       0
[EXPENSES-NET]                              20,105,073
[NET-INVESTMENT-INCOME]                     98,062,041
[REALIZED-GAINS-CURRENT]                        51,861
[APPREC-INCREASE-CURRENT]                            0
[NET-CHANGE-FROM-OPS]                       98,113,902
[EQUALIZATION]                                       0
[DISTRIBUTIONS-OF-INCOME]                        3,045
[DISTRIBUTIONS-OF-GAINS]                             0
[DISTRIBUTIONS-OTHER]                                0
[NUMBER-OF-SHARES-SOLD]                     85,641,586
[NUMBER-OF-SHARES-REDEEMED]                 86,164,131
[SHARES-REINVESTED]                            233,926
[NET-CHANGE-IN-ASSETS]                     126,768,536
[ACCUMULATED-NII-PRIOR]                              0
[ACCUMULATED-GAINS-PRIOR]                       51,861
[OVERDISTRIB-NII-PRIOR]                              0
[OVERDIST-NET-GAINS-PRIOR]                           0
[GROSS-ADVISORY-FEES]                       15,510,202
[INTEREST-EXPENSE]                                   0
[GROSS-EXPENSE]                             20,105,073
[AVERAGE-NET-ASSETS]                        17,700,537
[PER-SHARE-NAV-BEGIN]                            1.000
[PER-SHARE-NII]                                  0.000
[PER-SHARE-GAIN-APPREC]                              0
[PER-SHARE-DIVIDEND]                             0.000
[PER-SHARE-DISTRIBUTIONS]                            0
[RETURNS-OF-CAPITAL]                                 0
[PER-SHARE-NAV-END]                              1.000
[EXPENSE-RATIO]                                  0.500
[AVG-DEBT-OUTSTANDING]                               0
[AVG-DEBT-PER-SHARE]                                 0
</TABLE>