A simple, sensitive, selective and reproducible reversed-phase HPLC method was developed for the determination of sophoricoside in rat plasma after intravenous administration. Naringin was successfully used as internal standard (IS) for calibration. The chromatographic separation was accomplished on a reversed-phase C(18) column using acetonitrile-methanol-0.08% phosphoric acid (8:29:63, v/v/v) as mobile phase with a flow rate of 1.0 ml/min, with UV detection at 260 nm. Plasma samples were injected into the HPLC system after precipitating protein directly by methanol. Good linearity was achieved in the range of 0.0240 approximately 48.0 microg/ml (R(2)=0.9989). The limit of detection (LOD) and limit of quantification (LOQ) of this method were 0.0075 microg/ml and 0.0240 microg/ml, respectively. The absolute recoveries of sophoricoside from plasma were 95.8%, 93.2%, 98.0% at concentrations of 0.0240, 1.92, 15.0 microg/ml. The intra-day and inter-day variabilities were 3.39%~5.78% and 2.17%~4.72%, respectively. The developed method was successfully applied to the pharmacokinetic study of sophoricoside after intravenous administration of 2.5, 10 and 20 mg/kg in rats.