Objective:To investigate the antioxidative effect of Rosmarinic acid on kidney of mice with unilateral ureteral obstruction(UUO). Methods:Male C57BL/6J mice were randomly divided into 3 groups:Sham-operated group(n = 8), UUO model group (UUO model was established by ligating the left ureter, n = 24) and UUO+RA group(UUO model mice were treated with RA, n = 24). The latter 2 groups were divided into 3 subgroups according to times(3d, 7d and 14d) after intervention(n = 8). Mice underwent UUO were killed at 3, 7, 14 days. The time course of injurious process in mice with UUO were examined by histopathology; Western Blotting of Vimentin as well as E-cadherin were measured; Malondialdehyde(MDA), superoxide dismutase(SOD) contents in the homogenized lysate of obstructive renal cortex were determined. Results:Compared with those in Sham-operated group, from 3 to 14 day, injury of renal interstitum exacerbated gradually in UUO model group, Vimentin and MDA increased significantly, E-cadherin and SOD decreased significantly. Compared with those in UUO model group, Vimentin, E-cadherin, SOD and MDA showed no significant difference in UUO+RA group on 3d; Vimentin and MDA decreased, E-cadherin and SOD increased, renal interstitial fibrosis attenuated in UUO+RA group on 7d, till 14d. Conclusion:Rosmarinic acid may attenuated renal interstitial fibrosis in mice underwent UUO by reducing lipid peroxidation production and improving antioxidative enzyme contents.