Abstract: The work aims to study the drug metabolizing enzymes involved in the metabolism of butylphthalide and evaluate the induction and inhibition activities of butylphthalide on CYP450 isoenzymes by using in vitro (liver microsome incubation system of rats and human) and in vivo (CYP induced model of rats) method. Butylphthalide was incubated with selective inhibitors of CYP450, and its metabolic rate was determined to identify the metabolizing isoenzymes of NBP in rat (normal and induced rats) and human liver microsomes. The in vitro inhibition effect of butylphthalide on 6 main liver microsomal CYP450 isoenzymes was evaluated by using probe drugs; the induction and inhibition activities in vivo of butylphthalide on CYP450 isoenzymes were evaluated by NBP ig dosing (160 mg·kg^-1) and iv dosing (20 mg·kg^-1) in rats. After adding the specific inhibitors of CYP2C11, 2E1 and 3A1/2 for rat, CYP2C19, 2E1 and 3A4/5 for human, the metabolism of NBP in rat and human liver microsomes were reduced 38.8%, 86.2%, 78.4% and 51.0%, 92.0%, 58.9% of control, respectively. The metabolic rates of NBP in CYP2E1 and 3A1/2 induced rat liver microsomes were increased 25.5% and 68.9%. High concentration of NBP (≥200 μmol·L^-1, in vitro) could inhibit the activities of CYP1A2, 2C6, 2C11 and 2D2 in rats, and high concentration of NBP (≥15 μmol·L^-1, in vitro) could inhibit the activity of CYP2C19 in human. All the results indicated that NBP should be mainly metabolized by CYP2E1, 2C11 and 3A1/2 in rats and CYP2E1, 2C19 and 3A4/5 in human. High concentration of NBP could inhibit human CYP2C19 in vitro. No significant induction/inhibition effects of NBP were observed on rat liver CYP450 isoforms after ig 160 mg·kg^-1 NBP or iv 20 mg·kg^-1 NBP.