Abstract: ObjectiveTo investigate the metabolic mechanisms of chlorpyrifos-methyl in vitro of rat.MethodsMetabolic system was used to study the metabolic mechanism of chlorpyrifos-methyl.The protein concentration of tissue homogenates and cell fractions were determined according to the method of Lowry.The content of chlorpyrifos-methyl was determined by gas chromatography.In vitro metabolic test,chlorpyrifos-methyl and its metablites were assayed by high-performance liquid chromatography.ResultsChlorpyrifos-methyl was mainly metabolized in the liver of rats.In liver cells,the main place of metabolism of chlorpyrifos-methyl was hepatic microsomes and cytoplasm.The obvious oxidation of chlorpyrifos-methyl was catalyzed by microsomal enzymes.The different systems of biotransformation for chlorpyrifos-methyl existed in hepatic microsomes and cytoplasm.ConclusionThe most important site of metabolism of chlorpyrifos-methyl was hepatic microsomes and cytoplasm.The metabolic mode of chlorpyrifos-methyl was mostly oxidation reaction.