Objective To investigate the effects of triptolide on proliferation,apoptosis and the changes of Ski,Smad3,Smad7 and collagen type I(ColI) in cultured rat mesangial cells induced by transforming growth factor (TGF)-β1.Methods Cultured HBZY-1 rat mesangial cells were divided into 5 groups:(1)normal control group; (2)TGF-β1 group (10 μg/L); (3)-(5)triptolide (0.4,2,10 μg/L)+TGF-β1 (10 μg/L) groups.The cell proliferation was detected by MTT.Apoptosis of mesangial cells was detected by TUNEL assay.The expressions of Ski,Smad3,Smad7 mRNA were examined by real-time quantitative PCR.The expressions of Ski,Smad3,Smad7 and ColI protein were detected by Western blotting.The localizations of Ski and Smad3 protein were detected by laser confocal fluorescence microscope.Results Compared with the normal control,TGF-β1 (10 μg/L) significantly stimulated mesangial cells proliferation,while decreased apoptosis.The mRNA and protein expressions of Ski,Smad7,Smad3 and ColI protein expression in TGF-β1 group were increased (P ＞0.05).In comparison with TGF-β1 group,triptolide could significantly inhibit TGF-β1-induced mesangial cells proliferation in dose-dependent manner,and promote the apoptosis of mesangial cells.In TGF-β1 group,mRNA and protein expresscons of Ski and Smad7 were increased (P＜0.05),Smad3 mRNA and protein were decreased (P ＞0.05),and ColI protein was decreased (P＜0.01).In comparison with TGF-β1 group,fluorescence intensity of Ski,Smad3 proteins was significantly increased in cytoplasm,while decreased in nucleus.Conclusions Triptolide can inhibit TGF-β1-induced mesangial cells proliferation through regulating the expressions of Ski,Smad7 mRNA and protein,inhibiting Ski.Smad7 translocation to the nucleus,and down-regulating Smad3 mRNA and protein expression.Triptolide can promote apoptosis of mesangial cells.