To study a method for determination of sulfamethoxazole, sulfadiazine and trimethoprim tablets, a compound tablet of sulfamethoxazole, sulfadiazine and trimethoprim. METHOD: A capillary zone electrophoresis (CZE) method was used to assay three components of this compound preparation. RESULTS: The complete separation of components was achieved with 0.05 molL-1 pH 6.0 running phosphate buffer and a constant voltage of 20 kV (current of 95 μA～105 μA). The retention times of individual components were between three and eight minutes and a good linearity was shown between concentration and peak area in the concentration range over 70 μgml-1～750 μgml-1. When acetanilide was used as internal standard, the relative standard deviation (RSD) of each component determined in a batch was less than 1% (n=9). The recovery of each component was not less than 96.45% with RSD less than 3%. The analytical results obtained from 6 samples of clinical use were inconsistent with those by standard method, however the quantity of each sulfa drug was obtained by CZE method. CONCLUSION: The results showed this method is accurate, simple, and rapid. When this method is used, the quantity of each three components is determined, but by the standard method, only the total quantity of the two sulfa drugs is obtained.