Abstract: AimTo study the stereoselectivity of skin carboxylesterase metabolism and its molecular biological foundation for improving drug percutaneous absorption. MethodsKetoprofen ethyl ester was used as a model drug, and skin homogenate was applied for studying the stereoselectivity of carboxylesterase metabolism. Human liver L02 cell was used as control of carboxylesterase expression, and RT-PCR was used for studying the expression of carboxylesterase. ResultsThe main metabolite of ketoprofen ethyl ester in human skin homogenate was R-ketoprofen. Human carboxylesterase-2 was highly expressed in skin and its cells. However, the expression of human carboxylesterase-1 was very weak or not detectable. ConclusionHuman carboxylesterase-2 is the main hydrolytic enzyme of prodrugs in percutaneous absorption, and shows metabolic stereoselectivity to prodrugs with chiral esters.