OBJECTIVE: Rhein and angiotensin-converting enzyme inhibitor (ACEI) have been reported to prevent the progression of diabetic nephropathy (DN). We further explore the unknown ability to induce renal-protection of rhein and ACEI combined therapy in DN compared with the therapeutic effects of single treatment of them by using db/db mouse of type 2 diabetes model. METHODS: db/db and db/m mice, 8 weeks of age, were divided into five groups according to the following treatments: (A) db/m, given saline treatment; (B) db/db, given saline treatment; (C) db/db, given rhein treatment (150 mg/kg/day); (D) db/db, given benazepril treatment (10 mg/kg/day); (E) db/db, given rhein (150 mg/kg/day) with benazepril (10 mg/kg/day). Body weight, plasma glucose, plasma lipid and 24 h urinary albumin excretion levels were measured every 4 weeks. Morphometry of renal tissue and immunohistology of transforming growth factor-beta1 (TGF-beta) and fibronectin were determined for all groups at the end of the treatment. RESULTS: It was found that after treatment urinary albumin excretion was reduced after 4 weeks treatment in group E and after 8 weeks treatment in groups C and D, when compared to group B (p<0.05). Plasma creatinine levels dropped significantly for group E, compared with the diabetic control group by the end of the treatment period. Furthermore, after the treatment body weight, plasma glucose, cholesterol, triglyceride and low density lipoprotein all decreased in groups C and E compared to group B (p<0.05). Histological morphometric analysis revealed that the whole glomerular area and extracellular matrix area was significantly reduced in groups C, D and E compared to group B, at 20 weeks of age, an effect most pronounced in group E. Using immunohistochemistry, the expression of fibronectin and TGF-beta1 in groups C, D and E was found to have decreased compared to group B, after 12 weeks treatment, again the effect being more pronounced in group E. CONCLUSIONS: There appeared to be a similar renal protective effect of rhein compared with benazepril in diabetic nephropathy. A combined therapy may offer a more beneficial complementary effect on kidney injury in db/db mice, as reflected by urinary albumin excretion, renal function and histological changes. Our findings suggest that a therapeutic approach that combines rhein with ACEI provides a more effective therapy for DN than does either agent alone.