Paclitaxel is a substrate of the efflux transporters such as P-glycoprotein, and is mainly metabolized by the liver. Schisandrol B (Sch B), one of the active components in Schisandra, has been reported to be able to inhibit the activity of P-gp and CYP3A. It might be possible that Sch B would alter the pharmacokinetic behavior of paclitaxel. Therefore, the purpose of this study was to investigate the effect of Sch B on the pharmacokinetics of paclitaxel administered orally and intravenously in rats. Paclitaxel were administered to rats orally (30 mg/kg) or intravenously (0.5 mg/kg) with or without the concomitant administration of Sch B (10 or 25 mg/kg). Oral pharmacokinetic parameters of paclitaxel were significantly altered when pretreated with Sch B. There were significant increases in AUC0-24h (from 297.7±110.3 to 838.9±302.1 h*ng/ml; p<0.05) and Cmax (from 51.7±20.1 to 136.4±35.5 ng/ml; p<0.05) in the presence of Sch B (25 mg/kg). The pharmacokinetic parameters for i.v. paclitaxel were not significantly affected by Sch B in contrast to that of oral administration. Since the presence of Sch B enhanced the systemic exposure of paclitaxel, their pharmacokinetic interaction should be taken into consideration. As the oral bioavailability of paclitaxel was increased about 3-fold in the presence of Sch B, the concomitant use of Sch B may provide a benefit in the oral delivery of paclitaxel. Copyright © 2010 John Wiley & Sons, Ltd.