Objective To observe the protective effects of natural antioxidant tea polyphenols(TP) on myocardial free radical metabolic disorder in mice induced by inhalation of hypobaric pure oxygen under 5500 m hypobaric condition. Method Fourty-two male Kunming mice were randomly divided into three groups(n=14 each):group A, normal control; group B, inhalation of pure oxygen(>96%) at simulated altitude of 5500 m in an animal altitude chamber;group C(TP protection group), same as group B but 100 mg/kg of TP was given orally before the exposure. The exposure time was 2 h/d,3 d/wk for a total of 8 wk, and distilled water was given to groups A and B before exposure. After experiment, the mice were decapitated on the next day and the heart was quickly removed. Malondialdehyde(MDA) concentration, superoxide dismutase(SOD) activity and nitric oxide(NO) content were measured. In addition, Cu,Zn-SOD and inducible NO synthase(iNOS) enzymatic contents in myocardial tissue were qualitatively examined by immunohistochemical assaying. Result Compared with the control, MDA concentration, SOD activity and Cu,Zn-SOD enzymatic content in group B were significantly increased(P<0.05).But in TP protection group, myocardial MDA formation was significantly decreased(P<0.01) and SOD activity and Cu,Zn-SOD expression restored to normal. On the contrary, myocardial NO generation and iNOS expression were significantly reduced after repeated inhalation of hypobaric oxygen at 5500 m.NO metabolism regained to normal after repeated administration of TP. Conclusion Natural antioxidant TP had protective effects on myocardial free radical metabolic disorder induced by inhalation of hypobaric pure oxygen under 5500 m hypobaric condition.