Abstract: Objective To observe the effect of codonopsis pilosula(Enshi)on expression of oxygenfree-radical and tauprotein in gyrus hippocampi and cerebral cortex of rats with Alzheimer disease induced by okadaic acid.Methods The rat model of Alzheimer disease induced by okadaic acid was employed.Positive control and test group were injected with Vit.C.Codonopsis pilosula(Enshi)groups and control group's supreoxide dismutase(SOD),glutathione per oxidase(GSH-PX),malondialdehy de(MDA)and tauprotein in gyrus hippocampi and cerebral cortex were measured.Results In contrast with control groups,concentrations of SOD(114.98±22.90),GSH-PX(13.11±1.78)and SOD(159.94±14.67),GSH-PX (12.25±1.47)in cerebral cortex and gyrus hippocampi of rats with Alzheimer disease were lower(P<0.05,0.001).Concentrations of MDA(5.38±2.76),Tau(174.97±12.89)and MDA(4.81±1.54),Tau(148.61±10.77)in cerebral cortex and gyrus hippocampi of model rats were higher than that of control group(P<0.001).Concentrations of SOD,GSH-PX,M DA and tau protein showed statistically significant difference between high(750 mg)and moderate dose(500 mg)model group(P<0.05),and the difference between lower dose group(250 mg)and model group was not signifieant(P>0.05).Conclusion Codonopsis pilosula(Enshi)can up-regulate expression of SOD,GSH-PX and down-regulate expression of MDA and tauprotein in brain tissues of experimental rats.