Abstract: AimTo study the biliary excretion of genistein and its metabolite at different doses in rats. MethodsSuspended in 0.5% CMC-Na solution, genistein was orally administered to rats at the dose of 6.25, 12.5 and 50 mg·kg^-1, separately. At various time intervals, the bile was collected. The bile was treated with β-glucuronidase. The genistein in bile was extracted twice by vortexing with 2.0 mL mixture of methyl tert-tubtyl ether and pentane (8∶2). The organic phase was removed into the tubes and then evaporated in ventilation cabinet. The residue was dissolved in 50 μL of methanol. Twenty μL solution was drawn and detected by high-performance liquid chromatography. ResultsThe accumulative biliary excretion of genistein was (42.56±6.54), (75.17±18.87) and (126.60±34.78) μg at the dose of 6.25, 12.5 and 50 mg·kg^-1, respectively. The total drug (genistein plus glucuronidated genistein) excreted from bile was (108.46±35.23), (423.46±158.31) and (853.74±320.84) μg, and the ratio of glucuronidated genistein was 60.76%, 82.25% and 85.17% at the dose of 6.25, 12.5 and 50 mg·kg^-1, respectively. ConclusionThe genistein was excreted mainly in the form of glucuronidated genistein in rat bile. The genistein and glucuronidated genistein were excreted in a non-linear dose-dependent manner.