Objective To observe the dynamic changes of renin-angiotensinsystem,collagen I(CoI) and intercellular adhesion molecule 1(ICAM-1) in hmg tissue of neonatal rats with lung fibrosis induced by hyperoxia.Methods One hundred and twenty term neonatal Wistar rats were randomly assigned into model group and air control group.The model group was continuously exposed to hyperoxia (FiO2=0.9)for 21 days,and the air control group was exposed to room air(FiO2=0.21).On the Ist,3rd,7th,14th and 21st day of exposure,the subjects were sacrificed.And then,the protein levels of CoI,ICAM-1 were measured by enzyme-linked immunosorbentassay and angiotensinII(AngII) by radio-immunity technique,the activity of angiotensin-convertion enzyme(ACE) were measured by biochemistry analysator,and the mRNA expression of ACE,AngII,CoI was measured by RT-polymerase chain reaction.The changes of lung histomorphology were observed.Results The ACE,AngII,CoI and ICAM-1 protein lev els of model group were (249.20±20.19)μg/g,(838.22±197.75)μg/g,(539.85±81.03) μg/g and (577.06±61.17)μg/g on the 14th day respectively and in.eased significantly as compared to the air control group (P＜0.05),and the ACE,AngII,CoI mRNA expression of modal group also increased signficantly on the 14th day (P＜0.05).The ACE,AngII,CoI and ICAM-1 protein levels of model group were(249.20±20.19)μg/g,(838.22±197.75)μ/g,(539.85±81.03)μg/g and (577.06±61.17)μg/g on the 21st day and increased to the peak respectively(P＜0.05),and the ACE,AngII and CoI mRNA expression had the same changes as well.The histopathological examination demonstrated different degrees of fibrosis in the model group.Conclusion The ACE,AngII,CoI and ICAM-1 protein levels and their mRNA expression were increased significantly on the 14th and 21st day in lung tissue of neonatal rats with lung fibrosis induced by hyperoxia.The renin-angiotensin system played a role in lung fibrosis induced by hyperoxia.