Abstract: A high-performance liquid chromatography method was used to investigate the metabolic transformation characteristics of ilexsaponin A₁ by rat intestinal flora in vitro and in vivo.The HPLC separation was performed on a reversed-phase Kromasil 100-5 C₁₈column (250 mm×4.6 mm) at a temperature of 30 °C and the mobile phase system consists of acetonitrile and trifluoroacetic acid (0.02%) in water using a gradient elution with the flow rate of 1.0 mL/min.In vitro samples were prepared by incubating ilexsaponin A₁ with intestinal flora of rats.In vivo samples including feces and urine samples were collected individually after oral administration of ilexsaponin A₁ to healthy rats.Then the in vivo and in vitro metabolism of ilexsaponin A₁ was investigated using the established HPLC method.The results showed that ilexsaponin A₁ could be metabolized to its aglycone (ilexgenin A) by rat intestinal flora in vitro,and after incubating for 48 h,about 93.12% of ilexsaponin A₁ was metabolized to ilexgenin A.In vivo,ilexsaponin A₁ and its aglycone were found in feces,but not in urine.It was found that ilexsaponin A₁could be metabolized to its aglycone by intestinal flora in vitro and in vivo,and after oral administration about 89.85％ of ilexsaponin A₁ was exerceted as its prototype and metabolites.