Ojective To establish a rat model of hyperoxia induced acute lung injury. Methods Eighty healthy male SD rats were randomly divided into an air group and a hyperoxia group ( ≥95% O2 ) .Each group was further divided into 12 h, 24 h, 36 h, 48 h, 60 h subgroups. Arterial blood gas was monitored. Lung tissue was sampled for evaluation of lung wet to dry ratio, lung index, and pulmonary permeation index. Bronchoalveolar lavage fluid ( BALF) was collected for measurement of lactatedehydrogenase ( LDH) activity and white blood cell count ( WBC) . Results After hyperoxia exposure for 48 ～60 h, lung pathology showed alveolar structure disruption, lung parenchyma wrath bleeding and edema.Lung wet to dry ratio, lung index, pulmonary permeation index, LDH and WBC in BALF all increased significantly, peaked at 48 h and remained at high level at 60 h while PaO2 dropped progressively.Conclusion Exposure to ≥ 95% O2 for 48 ～60 h can successfully establish the rat model of hyperoxia induced acute lung injury.