Aim To study the biotransformation of gly-cyrrhizin in rat intestine-liver. Methods The in situ vascularly perfused rat intestine-liver model was estab-lished with a validated LC-MS/MS method for assay of the model perfusate glycyrrhizin and glycyrrhetinic acid. Results The steady state intestinal and liver ex-traction ratios in the once-through perfused rat intes-tine-liver model for glycyrrhizin were ( 4. 2 ± 0. 6 )%and (28. 0 ± 3. 0)%, respectively; the first-order ab-sorption rate constant for glycyrrhizin in the recircula-tion of perfusate to the intestine model was ( 0. 33 ± 0. 06 ) min-1;after intraduodenal administration of gly-cyrrhizin,the main active metabolite in was the perfu-sate glycyrrhetinic acid, which was also found in intes-tinal luminal fluids. Conclusions The first-pass effi-cacy of glycyrrhizin is obvious and there is only a small amount of metabolite in the intestinal mucosa cells;gly-cyrrhizin is metabolized by gut bacteria or liver cells af-ter oral administration;the in situ vascularly perfused rat intestine-liver model can be used in glycyrrhizin pharmacokinetic studies.