The aim of this study is to investigate the effect of naringin on the pharmacokinetics of tamoxifen in rats. Tamoxifen (10 mg/kg) was administered orally 0.5 h and 3 days after oral administration of naringin (5 mg/kg). The plasma concentrations of tamoxifen were increased significantly tv naringin compared to control. Absorption rate constant ($K_a$) of tamoxifen with naringin was increased significantly compared to that of the control. The areas under the plasma concentration-time curve (AUC) and the peak concentrations ($C_{max}$) of tamoxifen with naringin were significantly higher than those of the control. Consequently, the relative bioavailability (R.B${\%}$) of tamoxifen with naringin was 2-3-fold higher than the control, and absolute bioavailability (A.B${\%}$) of tamoxifen were significantly higher (p<0.05 with coadministration, p<0.01 with pretreatment) than those of the control. The increased bioavailability of tamoxifen in rats with naringin might be associated with the inhibition by naringin of an efflux pump P-glycoprotein and the first-pass metabolizing enzyme CYP3A4.