The cytochrome P450(CYP)enzymes,involved in the metabolism of therapeutic drugs,are the major determinants of drug halflife.Among 57 human P450s,CYP3A4 is the most abundant and the most important because it metabolizes the majority of administered drugs.In this review we provide an overview on recent progress in the CYP3A4 research,such as basic structure,active site,mechanism of action,genetic phenotypes,probe substrate,drug metabolism and so on.