Background The polymorphism of drug metabolism enzyme is an important factor leading to the obvious therapy reaction to drugs. Cytochrome P450 3A4 (CYP3A4), one of CYP 3A sub-family, is the main metabolism enzyme of many drugs. CYP3A4 gene polymorphism is the main reason that leads to interindividual differences of drugs metabolization. Objective This review was focused on the effects of CYP 3A4 gene polymorphism on drugs reaction in available literatures. Content CYP3A4 is the main microsomal cytochrome P450 enzyme which is mainly distributed in human liver and intestine. Its interindividual variations in gene structure, genetic polymorphism and enzyme activity may result in differences among races such as drug actions and adverse effects and even causes many diseases such as coronary heart disease and tumor.