Abstract: Cinnamic acid was found and identified as the main metabolite in rat plasma after oral administration of hapagoside.HPLC was used for the evaluation of pharmacokinetics of hapagoside and its main metabolite in rats;and the analytes were chromatographically separated with a C₁₈ column（250 mm×4.6 mm,5 μm）.The mobile phase was composed of methanol-H₂O-acetic acid (60∶40∶0.1) and UV detector was set at 279 nm.After ig administration,the t_maxand t_1/2of hapagoside were 0.47 ± 0.21 h and 4.96 ± 0.98 h (at the dose of 50 mg/kg),respectively.While the t_maxand t_1/2of cinnamic acid were 4.17 ± 1.39 h and 5.78 ± 2.67 h.After iv administration,hapagoside was eliminated rapidly (t_1/2=1.89 ± 0.32 h), while the elimination of cinnamic acid was similar to that via ig administration (t_1/2=5.16 ± 2.27 h).This result indicated that hapagoside was rapidly absorbed after ig administration, although its bioavailability was less than 5%.As the main metabolite of hapogoside in rat plasma, cinnamic acid appeared rapidly and eliminated slowly.