Obstructive nephropathy often leads to renal tubulointerstitial fibrosis. Understanding of the pathogenesis of renal tubulointerstitial fibrosis caused by obstructive nephropathy is crucial to the development of effective therapeutic drugs to improve the prognosis of the patients. Silymarin, a polyphenolic flavonoid extracted from plants, has been shown to exhibit antiinflammatory and antioxidant effects ameliorating liver and kidney damage. However, the effect of silymarin on renal fibrosis in obstructive nephropathy remains to be explored. In this study, we found silymarin improved interstitial fibrosis and apoptosis induced by TGF-β1 and ameliorated oxidative damage. Our data further confirmed that silymarin regulates the TGF-β1/ Smad3 signaling pathway, and therefore improves renal tubular interstitial fibrosis caused by obstructive nephropathy.