An improved method with derivatization and gas chromatography (GC) is described for the determination of captopril, an antihypertensive agent. The method is based on the derivatization of captopril with pentafluorobenzyl bromide in acetonitrile, using potassium carbonate as a base catalyst. Under a mild condition, the highly polar and nonvolatile captopril was derivatized into a derivative with suitable chromatographic properties. The resulting derivative was separated on an OV-1 column and monitored with a flame-ionization detector (FID). The linear range of the method for the determination of captopril was over 0.25-4.00 μmol. The detection limit (signal-to-noise ratio = 3) of captopril was about 40 nmol. The method was satisfactorily applied to the analysis of captopril in tablets.