<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000783740
<NAME> MFS SERIES TRUST X
<SERIES>
<NUMBER> 021
<NAME> EMERGING MARKETS DEBT FUND CLASS A
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 12-MOS
<FISCAL-YEAR-END> JUL-31-2000
<PERIOD-START> AUG-01-1999
<PERIOD-END> JUL-31-2000
<INVESTMENTS-AT-COST> 1340001
<INVESTMENTS-AT-VALUE> 1388990
<RECEIVABLES> 86319
<ASSETS-OTHER> 6076
<OTHER-ITEMS-ASSETS> 145
<TOTAL-ASSETS> 1481530
<PAYABLE-FOR-SECURITIES> 57724
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 3163
<TOTAL-LIABILITIES> 60887
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1305179
<SHARES-COMMON-STOCK> 119325
<SHARES-COMMON-PRIOR> 119430
<ACCUMULATED-NII-CURRENT> 84599
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (16816)
<ACCUM-APPREC-OR-DEPREC> 47681
<NET-ASSETS> 1420643
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 149288
<OTHER-INCOME> 0
<EXPENSES-NET> 0
<NET-INVESTMENT-INCOME> 149288
<REALIZED-GAINS-CURRENT> 190336
<APPREC-INCREASE-CURRENT> 37978
<NET-CHANGE-FROM-OPS> 377602
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (106759)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 6917
<NUMBER-OF-SHARES-REDEEMED> (19044)
<SHARES-REINVESTED> 12022
<NET-CHANGE-IN-ASSETS> 316573
<ACCUMULATED-NII-PRIOR> 60670
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> (206669)
<GROSS-ADVISORY-FEES> 10930
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 60104
<AVERAGE-NET-ASSETS> 1282188
<PER-SHARE-NAV-BEGIN> 8.52
<PER-SHARE-NII> 1.09
<PER-SHARE-GAIN-APPREC> 1.77
<PER-SHARE-DIVIDEND> (0.98)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 10.40
<EXPENSE-RATIO> 0.05
</TABLE>
