A sensitive and simple Gas Chromatographic-Mass Spectrometric method was developed and validated for the determination of captopril in human plasma. Thiosalicylic acid was used as an internal standard, and plasma extraction was performed by solid phase extraction. The limit of quantification was 0.5 ng/mL with signal to noise ratio greater than 5. The calibration curve was linear from 1 to 160 ng/mL with r2 greater than 0.99. The coefficient of variation for within and between assay imprecision of the standards and for the limit of quantification were ≤ 10 % and ≤ 7 %, respectively. The percentage of inaccuracy for within- and between-assay including lower and upper limits of quantitation were ≤ 8 % and ≤ 6 %, respectively. The absolute recovery of captopril and thiosalicylic acid in plasma were greater than 98 % and 99 %, respectively. The high sensitivity and accuracy of this method allowed us to measure low concentrations of captopril in plasma for bioequivalence studies in healthy subjects.