Docetaxel, frequently used for the treatment of breast cancer, is mainly metabolized via hepatic cytochrome P450 (CYP) 3A in humans and is also a substrate of P-glycoprotein (P-gp). Wogonin has been shown to be able to modulate the activities of CYPs and P-gp, and it could serve as an adjuvant chemotherapeutic agent. However, the impacts of co-administration of wogonin and docetaxel on their pharmacokinetics have not been studied because of a lack of an analytical method for their simultaneous measurement. In the present study, we established an HPLC-MS/MS method for simultaneous measurement of wogonin and docetaxel in rat plasma, and it was then utilized to explore the pharmacokinetics of wogonin and the herb-drug interactions between wogonin and docetaxel after their combined administration in rats with mammary tumors. The rats received 10, 20 and 40mg/kg wogonin via oral administration, with or without docetaxel intravenously administered at 10mg/kg, and the plasma concentrations of wogonin and docetaxel were measured using the established and validated HPLC-MS/MS method. The C-max and AUC(0-t) of wogonin were proportionally increased in the dose range from 10 to 40mg/kg, suggesting a linear pharmacokinetics of wogonin. Moreover, the C-max and AUC(0-t) of docetaxel and the AUC(0-t) of wogonin were increased after co-administration (p<0.05), indicating increased in vivo exposures of both wogonin and docetaxel, which might lead to an increase in not only therapeutic but also toxic effects. Thus the alterations of pharmacokinetics should be taken into consideration when wogonin and docetaxel are co-administered.