OBJECTIVE To investigate the absorption of gnsenoside Rg1 and Rb1 in Radix Gngseng at different intestine segments of rats and the influence of the drug solution concentration, pH, P-gp inhibitor. METHODS The intestine cannulation was performed for in situ recirculation. Gnsenoside Rg1, Rb1 and phenol red concentration in the flux were separately measured by the reversed phase HPLC and UV. RESULTS When the concentration was raised from 0.075-0.75 g L(-1) and 0.03-0.3 g L(-1), the uptake of ginsenoside Rg1 and Rb1 was separately linearly increased (r >0.999), and no changes of K(a) absorption fraction and t(1/2) are found. The pH of flux has no effect on drug absorption. Ginsenoside Rg1 can be absorbed in the whole intestine and no changes of K(a), absorption fraction and t(1/2) refound and all the parameters of ginsenoside Rb1 at jejunum are higher than that at ileum and duodenum (P <0. 5). Further more, P-gp inhibitor verapamil has obvious effect on the intestinal absorption of ginsenoside Rb1 (P <0.5) while it has no effect on ginsenoside Rg1. CONCLUSIONS The absorption of ginsenoside Rg1 and Rb1 in intestine of rat are first-order kinetics, the absorption mechanism is infered the passive diffusion. Ginsenoside Rg1 has no specific absorption locus in intestine of rat and ginsenoside Rb1 has specific absorption locus of jejunum. Meanwhile, ginsenoside Rb1 is the P-gp substrate, and could increase its fraction of bioavailability by corporation with P-gp inhibitor.