Abstract: Using 2,6-di-O-pentyl-3-O-butyryl-β-cyclodextrin as chiral stationary phase of capillary gas chromatography, four enantiomers of racemic methyl ester of permethrinic acid were baseline resolved at 120℃. The relative retention values ( α ) for the enantiomers of cis-and trans-methyl ester of permethrinic acid is 1.03 and 1.04, respectively. It is all larger than 1.02, which is the requirement for the determination of the optical purity ( e.e .%) of chiral compounds. So, the optical purity of four chiral permethrinic acid was determined successfully and conveniently.