Objectives:To evaluate lung injury mechanism in SD rat with nitrogen dioxide(NO2) exposure. 　Methods:In the test-control study, pulmonary malondialdehyde(MDA),glutathione(GSH) and total-antioxidant content(T-AOC) were determined in 10 SD rats with long-term NO2 exposure,10 SD rats with short-term NO2 exposure and 10 SD rats with fresh air as control. 　Results: Pulmonary MDA content was increased and T-AOC was decreased significantly in SD rat exposed to NO2. Pulmonary GSH was decreased significantly in long-term NO2 exposure group as compared with short-term NO2 exposure group and control group. 　Conclusions: Imbalance between oxidant and antioxidant was an important mechanism in the pathogenesis of oxidizing lung injury in SD rat with NO2 exposure.