Abstract: Objective: To study the pathophysiology process of endotoxin-induced early acute lung injury（ALI） in rabbits, and to research the protective effects of chloroquine on it. Methods: Rabbits were randomly assigned to three groups: control group, ET group, and ET+chloroquine group. ALI was induced by intravascular injection of ET （500μg/kg）. The arterial partial pressure of oxygen （PaO₂ ）, phospholipase A₂ （PLA₂ ）activities both in serum and lung tissue, lipid peroxide（LPO）contents and superoxide dismutase（SOD） activities in lung tissue were measured in our experiment. Electron microscope and light microscope were used to observe the pathological injuries in pulmonary tissue. Results: Compared with control group, rabbits treated with ET displayed PaO₂ decrease, leukocyte sequestration in lung tissue, PLA₂ activity increase both in serum and pulmonary tissues, the increase of pulmonary LPO contents （P＜0.05） and the decrease of SOD activities （P＜0.05）. Typical pulmonary histopathological injuries were presented in ET group. In chloroquine group, PaO₂ showed no decrease, PLA₂ activities both in serum and pulmonary tissue and LPO contents were lower than ET group （P＜0.05）, and SOD activities were higher than those of ET group （P＜0.05）. The pulmonary histopathological injuries of chloroquine group showed slightly. Conclusion: Intravascular injection of ET can be used to induce early ALI in rabbits, and PLA₂ activation and oxidative injury played important roles in the pathophysiology process of early ALI.Chloroquine can inhibit PLA₂ activation and oxidative injury, which can alleviate the degree of ET-induced early ALI in rabbits to some extent.