Abstract: OBJECTIVE To establish a method for the quantitative determination of optical isomer impurity in the intermediate of zofenopril calcium by GC with pre-column derivatization. METHODS Using D-(+)-2-Octanol as pre-column derivatization reagent, the optimal chromatographic separation was performed on Agilent DB-1701(30 m×0.53 mm, 1.0 μm) column with nitrogen as the carrier gas at a flow rate of 2.0 mL·min^-1, the detector temperature was at 250 ℃, the inlet temperature was at 200 ℃. The temperature program was used. The injection volume was 1.0 μL. RESULTS The calibration curve was good linear relationship in the range of 3.22-121.44 μg·mL^-1 for the optical isomer impurity (R)-(+)-3-benzoyl thiol-2-methyl propionate(r=0.995 2). The limit of quantification was 3.22 μg·mL^-1. The average recovery was 99.6%-102.4%. The RSD of intra and inter day were <2.0%. CONCLUSION The method is simple, specific and accurate with good repeatability, which can be used for the determination of optical isomer impurity in the intermediate of zofenopril calcium.