Objective. To observe the protective effects of natural antioxidant tea polyphenols (TP) on repeated mild hypobaric hypoxia induced pulmonary free radical metabolic disorder in mice. Method. Fourty-two male Kunming mice were randomly divided into three groups (n=14 each): normal control (A); 1500 in mild hypobaric hypoxia (B) and TP protection group (C). The exposure time in hypobaric chamber was 2 h/d, 3d/wk, 8 wk in total. Before hypoxic exposure, TP was orally given to group C at a dose of 100 mg/kg, while distilled water was given to the other two groups. After experiment, the mice were decapitated on the next day and the lung was quickly removed. The 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 lung were were qualitatively examined by immunohistochemical assaying. Result. Compared with the control group, pulmonary MDA concentration and NO content were significantly increased after chronic mild hypobaric hypoxic exposures (P<0.01) but the MDA formation and NO generation in TP protection group were restored to normal. Pulmonary SOD activity in group B tended to increase. Cu, Zn-SOD expression in endothelial cells of bronchioli and iNOS contents in endothelial cells of bronchioli and endothelial cells and smooth muscle cells in pulmonary interstitial vessels were significantly elevated after repeated mild hypobaric hypoxic exposure. These enzymatic abnormal expressions regained to normal after administration of TP. Conclusion. Natural antioxidant TP had protective effects on repeated mild hypobaric hypoxia induced pulmonary free radical metabolic disorder.