OBJECTIVE: To investigate the effect of transforming growth factor β1( TGF-β1) type Ⅰ receptor kinase inhibitor SB431542 on epithelial-mesenchymal transition( EMT) induced by paraquat in type Ⅱ alveolar epithelial cells A549. METHODS: A549 cells were randomly divided into control group,paraquat group and TGF-β1 blockade group,with3 samples in each group. The cells in the control group were cultured without any treatment,cells in paraquat group were stimulated by paraquat of a final concentration of 20 μmol/L,cells in TGF-β1 blockade group were treated with paraquat with a final concentration of 20 μmol/L and SB431542 with a final concentration of 20 μg/L. After 5 days,cultured cells were harvested and observed for morphologic and phenotypic characteristics using inverted phase contrast microscope and scanning electron microscope. Cell migration was assayed by Transwell chamber. The expression of target protein was detected by Western blot. The enzyme-linked immunosorbent assay was used to detect the TGF-β1 levels. RESULTS: Under inverted phase contrast microscope and scanning electron microscope,A549 cells in control group grew normally,cells in paraquat group changed from epithelial morphology to mesenchymal morphology,cells in TGF-β1 blockade group reversed to epithelial cell morphology. The results of cell migration showed that the number of cells in the paraquat group passed through the membrane was higher than that in the control group and TGF-β1 blockade group( P < 0. 05). The relative expression of E-cadherin and zonula occluden-1 in paraquat group was decreased( P < 0. 05),while the relative expression of vimentin,α-smooth muscle actin,type I collagen,the phosphorylation Smad and Mad related protein( p-Smad) 2 and p-Smad3 was elevated( P < 0. 05),compared to control group and TGF-β1 blockade group. The levels of total TGF-β1 and active TGF-β1 increased in paraquat group than that in control group( P < 0. 05). CONCLUSION: Paraquat induced EMT in A549 cells by activating TGF-β1/Smads signaling pathway. Early treatment with SB431542 can inhibit paraquatinduced EMT by blocking TGF-β1/Smads signaling pathway.