Aim:To identify metabolites of ginkgolide B in rat urine,the predominant metabo-lism of ginkgolide B and the major cytochrome (CYP) P450 enzymes responsible for the metabolism of ginkgolide B in rat liver microsomes.Methods:A liquid chromatography quadrupole mass spectrometer and liquid chromatography ion-trap-time-of-flight mass spectrometer with electrospray ionization in negative-ion mode were used for the structure elucidation of metabolites in rat urine and liver microsome incubation.Various selective CYP450 inhibitors were applied to inves-tigate their effects on the metabolism of ginkgolide B and the formation of the major metabolite in rat liver microsomes.Results:Three metabolites were identi-fied in rat urine.One hydroxyl metabolite of ginkgolide B were identified in rat liver microsomes,and quinidine uncompetitively inhibited the formation of the metabolite;its inhibitor constant (Ki) value for the inhibition of hydroxyl metabo-lite was estimated to be 8 μmol/L,whileα-naphthoflavone,ketoconazole,sulfaphenazole,and diethyidithiocarbamate had no inhibitory effects.Conclusion:Ginkgolide B was metabolized to its hydroxyl metabolite in rats,and CYP2D6 was the major rat CYP isoform responsible for the ginkgolide B metabolism in rat liver microsomes.