Abstract： AIM:To study the significance of c-Ski and Smad3 expression in skin fibroblast of rat at 24 h after induction by the high or low concentration of TGF-β1 in vitro.METHODS:The protein expression of c-Ski,Smad3,Cyclin D and mRNA expression of c-Ski,Smad3 were examined by Western Blot and Realtime PCR assays respectively.The transfection efficiency of the pcDNA3.0 vector was measured by β-gal method.Cell proliferation was determined by the measurement of BrdU incorporation into newly synthesized cellular DNA using a cell proliferation ELISA kit(Roche)induced by the high or low concentration of TGF-β1 with or without transfection of c-Ski plasmid and Smad3 plasmid respectively.RESULTS:The protein and mRNA expression of c-Ski and Smad3 were significantly increased at the low and at the high concentration of TGF-β1 respectively.The protein expression of Cyclin D was increased at the low concentration of TGF-β1,but decreased at the high concentration of TGF-β1.Moreover.c-Ski overexpression promoted fibroblast proliferation and abrogated bidirectional role of the hish or the low concentration of TGF-β1 on fibroblast proliferation,and Smad3 overexpression inhibited fibroblast proliferation and abrogated bi-directional role of the high or the low concentration of TGF-β1 on fibroblast proliferation. CONCLUSION:The c-Ski and Smad3 expression difierent change at 24 h after high or low TGF-β1 concentration in turn determines the proliferation role of fibroblast,and suggests an important role of c-Ski and Smad3 in the promoting or inhibiting effects of TGF-β1 on fibroblast proliferation.