Abstract: Objective To study oxidative damage and fibrosis of lung tissue caused by intratiracheally instilling Fe₂O₃ nanoparticles inrats.Methods Malerats were given different doses of 20 nm Fe₂O₃ and 280 nm Fe₂O₃ suspension by intratracheal instillation.Some rats were givensingle-exposure then sacrificed at the end of 7 days.The other rats were repeatedly exposed and sacrificed at the end of 30 days.Super oxide dismutase(SOD),malondia ldehyde(MDA),glutathione-peroxidase(GSH-Px),and hydroxyp roline(HYP)intissue of the rats were detected.Results The levels of SOD(32.5±3.8 U/mg prot),MDA(2.29±0.18 nmol/mg prot)and GSH-Px(80.4±9.61 U/mg prot)in the lungtissue of the rats in high-dose group(20 nm Fe₂O₃)were significantly different form those of control group(P<0.05).The levels of SOD,MDA and GSH-Px inlungtissue of the rats in high-dose of 20 nm Fe₂O₃ group were significantly higher than those of high-dose of 280 nm Fe₂O₃ group,except GSH-Px in the rats of 30 days exposure,indicating severe damage caused by Fe₂O₃ nanoparticles.The levels of MDA and GSH-Px in the rats of high-dose group showed significant difference between the groups of 7 days'e and and 30 days' exposure.Conclusion The oxidative damage caused by 20 nm Fe₂O₃ in rat lungs is more serious than that caused by the 290 nm Fe₂O₃.Noobvious fibrosis is found.