To observe the inhibitory effects of Pterostilbene(PTE)on Epithelial-to-mesenchymal transition(EMT)in bleomycin-induced pulmonary fibrosis in rats and its possible mechanism.Methods:A total of 40 SD rats were randomly divided into 4 groups：a normal group，a model group，a PTE group and a prednisone group.Except for the normal group，the rat pulmonary fibrosis model was prepared by intratracheal injection of bleomycin solution.30 mg/(kg·d)of PTE was given to the PTE group，3 mg/(kg·d)of prednisone was given to the prednisone group，and the normal group and the model group were given the same amount of DMSO for 21 days.Take the lung tissue and stain it with Sirius scarlet to observe the distribution of collagen type Ⅰ(Collagen Ⅰ)and collagen type Ⅲ(Collagen Ⅲ)in rat lung tissue.Immunohistochemistry and PCR detected the expression of a-SMA，E-cadherin and Vimentin in rat lung.Results:Compared with normal group，the distribution of Col-Ⅰand Col-Ⅲ in the model group were increasing.Vimentin，a-SMA higher protein and mRNA expression were rising.The expression of E-cadherin protein and mRNA decreased.Compared with the model group，the distribution of type Ⅰ and type Ⅲ collagen in the drug group was reduced，and at the same time the mRNA of E-cadherin and protein expression levels were up-regulated，and the mRNA of α-SMA、Vimentin and protein expression level were inhibited.Conclusion:PTE can effectively alleviate the fibrosis process of pulmonary fibrosis rats.The mechanism may be related to the inhibition of collagen formation and the regulation of the expression of EMT-related molecules.