Abstract: ob＜x＞jective: To investigate the effect of tetrandrine (TET) on intestinal absorption by regulating the function of P-glycoprotein (P-gp). Method: The effects of TET on the intestinal absorption of a P-glycoprotein substrate, rhodamine123 (Rho123) and 5(6)-carboxyfluorescein (CF), were examined by an in vitro diffusion chamber system. Results: It was shown that TET might have the activity of inhibiting P-gp function in the intestine. And the paracellular pathway were not the main reasons of enhanced absorptive transport of these P-gp substrates in the presence of TET. Conclusion: TET may inhibit the activity of P-gp in the intestine. TET can promote the absorption of oral tumor drugs and inhibit the occurrence of multidrug resistance.