Abstract:Objective: To investigate the absorption mechanism of genistein self-microemulsifying system in rat intestines. Method: The concentrations of phenol red and genistein by in situ perfusion in rats were determined by UV and HPLC, respectively. The effects of drug concentrations, pH, various intestinal segments and P-glycoprotein (P-gp) inhibitor verapamil on the absorption had been studied. Result: The absorption rate constant (Ka) of genistein had no significant difference at concentrations of 0.05～0.5 mg·mL-1 and pH of 5.4～7.8 in perfusion. It was Ka of jejunum>ileum>duodenum>colon. The absorption of genistein in jejunum had significant difference (P<0.05) compared with other parts of intestines. Ka was increased obviously when verapamil was coperfused with genistein (P<0.05). Conclusion: The absorption of genistein self-microemulsifying system is a first order process with passive diffusion mechanism related to P-gp efflux. It can be absorbed at all segments of rat intestine， and the jejunum is the best absorption segment. pH had no special effect on the absorption of genistein self-microemulsifying system in rat intestime.