AIM: To investigate the effects of long-term tea polyphenols (TPs) consumption on hepatic microsomal drug-metabolizing enzymes and liver function in rats. METHODS: TPs were administered intragastrically to rots at the doses of 833 mg.kg.^-1d^-1 (n=20) and 83.3 mg.kg^-1.d^-1(n=20) respectively for six months. Controlled group (n=20) was given same volume of saline solution. Then the contents of cytochrome P450, b5, enzyme activities of aminopyrine N-demethylase (ADM), glutathione S-trasferase (GST) and the biochemical liver function of serum were determined. RESULTS: The contents of cytochrome P450 and bs in the livers of male rats in high dose groups (respedJvely 2.66±0.55,10.43±2.78 nmol.mg MS pro^-1) were significantly increased compared with the control group (1.08±1.04, 5.51±2.98nmol.mg MS pro^-1; P