Objective : To observe the effect of hydrogen sulfide( H2 S) 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 7th , 14th and 28th 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 7th , 14th and 28th 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 28th 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 7th , 14th and 28th day(P < 0. 05) , but the expression levels of E ⁃Cad in⁃NaHS + bleomycin group and prednisolone + bleomycin group were higher than that in bleomycin group at each time(P < 0. 05) , which was significant at 28th day in NaHS + bleomycin. Conclusion H2 S can reduce the degree of pulmonary fibrosis in rats , its mechanism may be related to the down⁃regulation of TGF⁃ β1and the inhibition of the EMT , which can enhance the expression of E ⁃cad and reduce the expression of TGF⁃ β1 , VIM and α ⁃SMA.