〔Abstract〕 Objective To observe the effect of hydrogen sulfide(H2S) on the expression of transforming growth factor-β1(TGF-β1),E-cadherin(E-CAD), Vimentin(VIM), alpha-smooth muscle actin(α-SMA) during epithelial-mesenchymal transformation(EMT), and to explore the anti-fibrosis mechanism of it. Methods Sixty rats(male SD)were randomly divided into control group, bleomycin group, NaHS+bleomycin group and prednisolone+bleomycin group, 15 rats per group.5 rats of each group were sacrificed at random in 7 th, 14 th and 28 th day. The degree of alveolitis and pulmonary fibrosis was observed.The expression of protein and mRNA of TGF-β1,E-cad, VIM,α-SMA were determined by Immunohistochemi stry and RT-PCR. Results (1) HE and Masson staining showed that the lung tissue of fibrosis had the lowest degree in control group. and the most severe in bleomycin group.The lung tissue of NaHS+bleomycin group and prednisolone+bleomycin group also had alveolitis and fibrosis changes, but the degree Were significantly less than bleomycin group.(2) The mRNA and protein expression levels of TGF-β1, VIM and α-SMA in bleomycin group, NaHS+bleomycin group and prednisolone+bleomycin group were all higher than that in control group at 7 th, 14 th and 28 th day(P<0.05), while the expression levels of them in NaHS+bleomycin group and prednisolone + bleomycin group were all lower than that in bleomycin groupat each time(P<0.05), which was significant at 28 th day in NaHS+bleomycin.(3) The mRNA and protein expression levels of E-Cad in bleomycin group, NaHS+bleomycin group and prednisolone + bleomycin group were all lower than that in control group at 7 th, 14 th and 28 th day(P<0.05), but the expression levels of E-Cad inNaHS+bleomycin group and prednisolone+bleomycin group were higher than that in bleomycin group at each time(P<0.05), which was significant at 28 th day in NaHS +bleomycin. Conclusion H2S can reduce the degree of pulmonary fibrosis in rats, its mechanism may be related to the down-regulation of TGF-β1 and the inhibition of the EMT, which can enhance the expression of E-cad and reduce the expression of TGF-β1,VIM and α-SMA.