OBJECTIVE: To investigate the effects of Fuzheng Huayu Recipe on renal interstitial fibrosis in rats induced by the toxic substances. METHODS: Forty Wistar rats were divided into 3 groups, including the normal group, model control and Fuzheng Huayu Recipe treated group. The renal fibrotic model was induced with intraperitoneal injection of dimethylnitrosamine (DMN) for 4 weeks and oral administration of food containing heavy metals such as Hg, etc for 8 weeks. From the 5th week, the rats were orally administered Fuzheng Huayu Recipe for 4 weeks. The renal tissue was stained with HE and periodic acid-silver metheramine, respectively. The serum creatinine and urea nitrogen were assayed with the kits, and the renal hydroxyproline (Hyp) contents in the homogenate of kidney tissue were measured with HCl hydrolysis. RESULTS: In the model group, the renal tubule was swollen, and the tubular epithelial cells were degenerated, necrosed and detached, with the infiltration of inflammatory cells; the tubular interstitium was expanded, characterized with the deposition of large collagens; the tubular basement membrane became thicker and wrinkled; and the renal Hyp content and serum creatinine and urea nitrogen levels increased remarkably as compared to the normal group. After the treatment with Fuzheng Huayu Recipe, the renal tubular inflammation and interstitial collagen deposition were alleviated, and the serum creatinine and urea nitrogen levels decreased significantly as compared to the model group. CONCLUSION: Administration of DMN and heavy metals can induce the renal interstitial fibrosis and impair the renal function. Fuzheng Huayu Recipe can improve the impaired renal functions and reverse the renal interstitial fibrosis.