to observe the protection of Warming Yang and Activating Blood Formula on renal interstitial fibrosis in rats and try to find the mechanism. Methods:The model of renal obstruction was established by unilateral ureteral obstruction (UUO) in rats, and then randomly divided into four groups, i.e. UUOW group (treated with the formula), UUOF group (treated with Fosinopril), UUO group and the sham-operation group. The morphological changes in obstructing renal tissue and the protein expressions of MMP-3, TIMP-1, FN were observed and compared. Results:Different degrees of kidney lesion were shown in UUO, UUOW, UUOF groups as compared with the SH group. The expressions of MMP-3, FN of UUO were higher than those of the SH group (P<0.05), and TIMP-1 was higher than MMP-3. Expressions of MMP-3 of both UUOF and UUOW had higher MMP-3 expression (P<0.05) and lower TIMP-1, FN expression than the UUO group(P<0.05). However, there were no significant difference among two treatment groups in all parameters (P>0.05). Conclusion:the formula may regulate the ratio between MMP-3/TIMP-1 by decreasing the expression of TIMP-1and increasing MMP-3, in that way protect renal tubule and delay the progression of renal interstitial fibrosis.