AIM: To study whether Smads signaling pathway was involved in human fetal lung fibroblast-myofibroblast differentiation induced by transforming growth factor (TGF)-β1 and the role of interferon (IFN)-γ, dexamethasone (DEX)in the fibroblast-myofibroblast differentiation. METHODS: α-Smooth muscle actin (α-SMA), Smad2/3, and Smad7protein were assessed by Weste blot. Collagen protein was analyzed by measuring hydroxyproline. α-SMA and collagen Ⅲ mRNA were assessed by RT-PCR. Myofibroblasts morphology and Smad2/3 nuclear translocation were assessed by immunohistochemistry. The overexpression of Smad7, a negative mediator of Smads signaling pathway, was acquired by transfection of Smad7 vector. RESULTS: During fibroblast-myofibroblast differentiation induced by TGF-β1, IFN-γ 200 μg/L markedly blocked TGF-β1-induced α-SMA protein expression (P＜0.01),collagen protein (P＜0.01) and mRNA (P＜0.05) expression, and myofibroblasts morphological transformation, but DEX 10 μmol/L augmented TGF-β1-induced α-SMA expression (P＜0.01). For myofibroblasts, both IFN-γ 200 μg/L and DEX 10 μmol/L did not inhibit α-SMA expression (P＞0.05) and collagen protein (P＞0.05) and mRNA expression (P＞0.05) and did not change myofibroblasts morphology. Transient transfection of Smad7 vector resulted in significant inhibition of TGF-β1-induced α-SMA expression (P＜0.01). IFN-γ 200 μg/L did not block TGF-β1-stimulated Smad2/3 phosphorylation and their nuclear translocation. CONCLUSION: TGF-β1 induced fibroblastmyofibroblast differentiation in a Smad proteins-dependent manner. IFN-γ could block this process but it was not mediated by interrupting smad2/3 phosphorylation and their nuclear translocation and DEX played a synergism with TGF-β1. Differentiated myofibroblasts, however, were resistant to both IFN-γ and DEX.