Objective: To investigate the antioxidant effects of Bach1 siRNA on BLM induced pulmonary Fibrosis.Methods: Mouse lung fibroblasts(MLF)were incubated with TGF-β1(5ng/ml)and subsequently infected with Bach1 siRNA.Pulmonary fibrosis models of mice were induced by bleomycin(BLM)and Bach1 siRNA(1 × 109 PFU)was administered by tail vein subsequently.The mRNA and protein expression of Bach1 and antioxidant factors such as heme oxygenase-1(HO-1),glutathione peroxidase 1(GPx1)and NAD(P)H:quinone oxidoreductase 1(NQO1)were determined by RT–PCR and western blot.Changes of fibrosis-related cytokines including TGF-β1 and IL-6were determined by ELISA.Histological changes of lung tissues were stained with H&E and Massons.Results: MLF cells administered with Bach1 siRNA promoted the mRNA and protein expression of HO-1 and GPx1,but inhibit the levels of TGF-β1 and interleukin-6 IL-6in cell supernatants compared with TGF-β1 group; Bach1 siRNA enhanced the expressions of antioxidant factors,but suppressed fibrosis-related cytokines in mice compared with BLM group.Finally,inflammatory infiltration of alveolar and interstitial,destruction of lung structure were significantly attenuated in mice with Bach1 siRNA compared with BLM group.Conclusion: Bach1 siRNA may exert protective effects on BLM induced pulmonary fibrosis in mice.