Objective To observe the effect of curcumin on the expression of smad7 and TGF-β1 in rats renal tubular cells of with Ang II, and discuss the mechanism of curcumin to improve renal interstitial fibrosis.Methods Cultured rat renal tubular epithelial cells were divided into the blank group, the Ang II control group and the low, medium and high dose curcumin group. The rest of the groups were intervened by 10-8 mol/L Ang II except the blank group; the low, medium and high dose groups of curcumin were intervened by 2.5, 5.0, 10.0μmol/L curcumin. Then Western blot was used to detect the expression of TGF-β1 and smad7 protein, RT-PCR was used to detect the TGF-β1 and smad7 mRNA expression.Results Compared with the blank group, the expression of TGF-β1 protein (0.23 ± 0.03vs. 0.16 ± 0.01), and TGF-β1 mRNA (1.89 ± 0.20vs. 1.00 ± 0.00) significantly increasedin AngⅡ control group (P<0.05), and the expression of smad7 protein (0.19 ± 0.03vs. 0.24 ± 0.02), and smad7 mRNA (0.48 ± 0.05vs. 1.00 ± 0.00) significantly reduced in AngⅡcontrol group (P<0.05). Compared with the AngⅡ control group, the expression of TGF-β1 protein in low, medium and high dose curcumingroup (0.18 ± 0.02, 0.17 ± 0.02, 0.16 ± 0.03vs. 0.23 ± 0.03) and TGF-β1 mRNA (1.58 ± 0.11, 1.34 ± 0.16, 0.97 ± 0.19vs. 1.89 ± 0.20) significantly decreased (P<0.05), and the expression of smad7 protein (0.28 ± 0.04, 0.31 ± 0.03, 0.34 ± 0.04vs. 0.19 ± 0.03) and smad7 mRNA (0.68 ± 0.07, 0.80 ± 0.06, 0.98 ± 0.09vs.0.48 ± 0.05) increased significantly (P<0.05).Conclusions Curcumin can thus play its role in renal protection by counteract the AngⅡ mediated renal interstitial fibrosis. Its mechanism may be related to the reduction of TGF-β1 protein and its mRNA expression, up regulation of smad7 protein and its mRNA expression.