Abstract: Objective: To investigate the changes of serum neutrophil elastase（NE） in rabbits with acute lung injury（ALI） induced by endotoxin and the effect of hemin.Methods: 24 male New-Zealand rabbits were divided into three groups: control group（A）,endotoxin-treated group（B） and endotoxin plus hemin treated group（C）.ALI models of rabbits were replicated with intravascular endotoxin injection（700 μg/kg）.Vital sign,arterial blood gas and serum NE concentration were recorded at 0,0.5,1,2,4 h.After 4 h,the rabbits were sacrificed,pathological changes of lung tissue and the dry-to-wet lung weight ratio was examined.Results: After infusion of endotoxin,in group B,respiratory rates significantly increased and blood presser,oxygenation index decreased,the serum NE was absolutely higher compared with group A and C at 1 hour（P＜0.01）,the dry-to-wet lung weight ratio was significantly lower than that in group A（P＜0.01）,Pulmonary edema,hemorrhage were observed.In group C,the serum NE and the dry-to-wet lung weight ratio had no differences compared with group A（P＞0.05）.Conclusion: Serum NE concentration was obviously increased in endotoxin-induced ALI,the upregulation of heme oxygenase by hemin could decrease NE to protect the lung tissue.