Objective To investigate the expression of periostin in the kidneys of rats with obstructive nephropathy and its relevance to renal interstitial fibrosis.Methods Eighteen male adult SD rats were randomly divided into sham group,model group and benazepril group (6 in each group).Unilateral ureteral obstruction (UUO) model was induced by ligating the left ureter of rats.RT-PCR was used to detect the mRNA expressions of periostin and TGF-β1,and ELISA to detect the protein expression of periostin,Ang Ⅱ,and TGF-β1 in kidney tissue.Pathological changes of renal tissue were observed by HE and Masson staining.The protein expression of collagen Ⅰ (Col Ⅰ ) in kidney tissue was examined by immunohistochemical staining.Results The mRNA expressions of periostin and TGF-β1 in model group increased markedly as compared with sham group (all P＜0.05),and benazepril could decrease these mRNA expressions (all P＜0.05).The protein expressions of periostin,Ang Ⅱ and TGF-β1 in kidney tissue were significantly increased in model group as compared with sham group (all P＜0.05),and benazepril could decrease these protein expressions (all P＜0.05).The expression of periostin in kidney tissue was positively correlated with the expressions of Ang Ⅱ,TGF-β1 and Col Ⅰ,as well as the degree of renal interstitial fibrosis (r=0.652,0.781,0.776 and 0.825 respectively,all P ＜0.05).Conclusion Periostin expression is up-regulated in kidney tissue of rats with obstructive nephropathy,which is associated to the over-deposition of extracellular matrix (ECM) in the kidneys of UUO rats.