Abstract: Objective:To observe changes of maleic dialdehyde（MDA） levels and superoxide dismutase（SOD） activities,and to study the effect of oxidative stress reaction in pathogenesis of endotoxin（ET）-induced acute lung injury（ALI） in rabbits.Methods: 24 Flap-eared white rabbits were randomly assigned to three groups:control group,ET-treated group and combination group（treated by ET and naproxen）.ALI was induced by intravenous injection of ET（600 μg/kg） by jugular vein.Changes of respiratory rate,heart rate and blood pressure were monitored during the experiment.Arterial blood gases and levels of endothelin-1（ET-1）in serum were measured in designated time.When rabbits were killed at 240 minutes of the experiment,0.2g weight of right lung diaphragmatic lobe was used to measure MDA levels and SOD activities.The pathologic changes of pulmonary tissues were examined with microscope and the ratio of lung's wet/dry（W/D） was measured.Results: Compared with control group,rabbits of ET-treated group showed blood pressure,heart rate decreased and the respiratory rate increased;PaO₂ decreased,levels of ET-1 increased;In lung tissues,levels of MDA increased and activities of SOD decreased.pathological examination showed obviously injuries in pulmonary tissues;the ratio of W/D was increased in ET-treated group.Corresponding items of combination group were samilar to those in control group;injuried degree of lung tissue was slighter.Conclusion: Strong oxidative stress is found in lung tissues of rabbits with ALI,and body's anti-oxidative stress abilities is deficient relatively at the same time.