Objective To investigate the expression of p21 and p53 in renal interstitial fibrosis rats and the effect of enalapril on it. Methods Sprague-Dawley rats were randomly divided into 3 groups, shame operation rats group, unilateral urethral obstruction and enalapril treatment group. Histological chan-ges were observed by Masson stain. The expression of p21 mRNA and p53 mRNA was detected by RT-PCR. Results With degree of interstitial fibrosis aggravating, the expression of p21 and p53 increasing,p21 and p53 expression of UUO rats at every time point were positive correlative. Enalapril can inhibit the expression of p21 and p53. Concinsion p21 and p53 expression increased in UUO rats renal cortex and enalapril can significantly inhibit its expression, p21 may participate in the pathogenesis of renal tubule-in-terstitial fibrosis through p53 pathway.