Objective To observe the effect of stageⅢdiabetic nephropathy(DN)treated by Qizhi Jiangtang capsule and explore its potential mechanism. Methods According to digital table method,the patients who conformed to the diagnostic criteria of stageⅢDN were randomly divided into two groups:an experiment group and a control group. All the patients in the two groups took elution treatment for 2 weeks,and then were treated with western basic therapy. The patients in the experiment group were administered orally with Qizhi Jiangtang capsule(2.5 g once, 3 times a day),while those in the control group treated with valsartan 80 mg,once a day. Urine microalbumin(mALB), mALB/urine creatinine(UCr),β2-microglobulin(β2-MG),α1-microglobulin(α1-MG)were observed in the two groups,endothelin-1(ET-1),nitric oxide(NO),thromboxane B2(TXB2),6-keto prostaglandin F1α(6-keto-PGF1α) were also determined. Serum creatinine(SCr),blood urea nitrogen(BUN),serum cystatin-C(Cys-C),retinol-binding protein(RBP),β2-MG were detected in the blood biochemistry automatic analyzer. These laboratory markers were inspected before treatment and at the 4th,8th and 12th week after treatment. Results Ninety-six patients in the experiment group and 95 patients in the control group were effectively included in the end. Before treatment,there were no statistic significant differences in urine mALB,mALB/UCr,β2-MG,α1-MG and blood ET-1,NO,TXB2, 6-keto-PGF1α between two groups(all P>0.05). Along with the prolongation of treatment,urine mALB,mALB/UCr,β2-MG,α1-MG and ET-1,TXB2 were significantly reduced,while NO,6-keto-PGF1α were significantly raised in the two groups after treatment,and the above changes in the experimental group were more obvious. There were statistic significant differences of mALB,mALB/UCr,β2-MG,α1-MG and TXB2,6-keto-PGF1αbetween two groups at the 12th week after treatment〔mALB(mg/L):36.6±9.2 vs. 78.6±16.5,mALB/UCr(mg/mmol):3.90±1.97 vs. 9.70±2.90,β2-MG(mg/L):0.25±0.10 vs. 0.40±0.12,α1-MG(mg/L):8.40±2.26 vs. 12.50±3.21,TXB2 (ng/L):75.8±18.7 vs. 94.7±21.7,6-keto-PGF1α(ng/L):73.4±15.2 vs. 65.2±11.5,P<0.05 or P<0.01〕. But there were no statistic significant differences of ET-1 and NO between experimental group and control group at the same time-points〔ET-1(ng/L):57.6±6.9 vs. 59.1±6.2,NO(μmol/L):68.9±11.6 vs. 65.4±10.7,both P>0.05〕. In each of the two groups,the comparisons of the levels of SCr,BUN before and after treatment,there was no statistical significant difference at any time point;the same comparisons between the two groups,there was also no statistic significant difference before treatment and at each of the same time-point after treatment(all P>0.05). The levels of Cys-C,RBP andβ2-MG of the control group after treatment had the tendency of decreasing,but no statistic significant differences were found(all P>0.05). The levels of Cys-C,RBP,β2-MG of the experimental group at the 12th week after treatment were significantly lower than those before treatment〔Cys-C(mg/L):0.72±0.07 vs. 0.89±0.12,RBP (mg/L):53.0±14.2 vs. 66.1±16.5,β2-MG(mg/L):1.86±0.71 vs. 2.79±0.82,all P<0.05〕. Conclusions Qizhi Jiangtang capsule can significantly reduce the levels of urine mALB and mALB/UCr of patients with stageⅢDN and stabilize their renal functions;its therapeutic effect is better then that of valsartan. Its mechanisms are related to the reduction of ET-1,elevation of NO,maintenance of dynamic equilibrium of thromboxane A2/prostacycline(TXA2/PGI2) and protection of vascular endothelial cells.