Determination of the content of cefalexin and trimethoprim in the compound cafalexin capsules by RP-HPLC was improved and was compared with solvent extraction method. The chromatog. conditions were: mobile phase 0.025 mol/L phosphoric acid (pH = 3.0 modulated by 20% NaOH)-acetonitrile, ODS C18 column, column temperature 40 degree, flow rate 1.0 mL/min, detection wavelength 235 nm. The results showed that the linear range for cefalexin and trimethoprim was 10-150 μg/mL (r = 0.99996), 2-30 μg/mL (r = 0.99996), resp. The average recoveries were 99.94% (RSD = 0.5%), 99.47% (RSD = 0.4%), resp. The results by HPLC was close to that by solvent extraction method. The method HPLC is simple, rapid, accurate and sensitive.