Objective：To investigate the effects of Tamoxifen on renal interstitial fibrosis in UUO rats. Methods：Feamale SD rats were divided into 3 groups at random：①UUO group（6 rats）, ②the treated group（6 rats）：UUO + Tamoxifen 10 kg／（mg·d） day by gastrogavage, ③sham operated group（6 rats）. Kidney were harvested at day 9 after UUO. The renal tissues were examined by HE，PAS and Masson. Tissue α-SMA protein expression was determined by Immunohistochemistry. Results：UUO for 9 days significantly activated α-SMA protein expression, induced interstitial fibrosis and tubulointerstitial lesion in obstructed kidney of UUO group， compared with sham operated group rats. Conversely daily administration of Tamoxifen significantly inhibited α-SMA expression and decreased interstitial fibrosis and tubulointerstitial lesion in obstructed kidney of treated group. Conclusion：Tamoxifen had beneficial effects on reduction of renal interstitial fibrosis in SD rats with UUO, and this effect may be associated with Tamoxifen inhibits α-SMA expression.