Abstract: Carboxylesterases (CESs) belong to the esterase family, which are mainly responsible for catalyzing metabolism of a variety of drug as well as endogenous and exogenous compounds. CESs are widely distributed in the body, mainly expressed in lung, liver, intestine, kidney, skin epithelial cells, etc. There are significant species differences in the expression of CESs, which results in the difference on the drug metabolism with genetic polymorphism. In this paper, an overview of the classification and distribution, physiological function and mechanism, species differences and gene polymorphism of CESs are provided for the research of CESs and drug design.