We investigated the effect of Apocynum venetum L. extract (AV) on the activity of cytochrome P450 (CYP) 3A and P-glycoprotein (P-gp). The plasma concentration of nifedipine (NF), which is a substrate for CYP3A, did not change after oral administration with AV (3.3 mg/kg). Also, AV (3.3 and 33 mg/kg) did not affect the intestinal absorption of NF. In the rats treated with multiple administrations (15 mg/kg/d) of St. John's wort extract (SJW) for 2 weeks, the plasma concentration of NF after oral administration was significantly decreased. On the other hand, there was no significant differences in the pharmacokinetic parameters of NF between AV-treated (3.3 mg/kg/d) and none-treated rats. Furthermore, the intestinal absorption of methylprednisolone, which is a substrate for P-gp, was not affected by AV treatment for 2 weeks. These results suggest that, unlike SJW, the recommended dose of AV (3.3 mg/kg/d) would not influence hepatic CYP3A and intestinal P-gp in rats.