OBJECTIVE: To explore the effects of Salvia miltiorrhiza on renal morphology and renal function of rats with streptozotocin diabetes. METHODS: Thirty male Wistar rats were randomly divided into three groups, which were normal control group, untreated group and Salvia miltiorrhiza-treated group. Diabetic nephropathy was induced in rats of the last two groups by intraperitoneal injection of streptozotocin after unilateral nephrectomy. Then the rats in the normal control and untreated groups were fed with normal saline while those in the Salvia miltiorrhiza-treated group were fed Salvia miltiorrhiza preparation for 8 weeks. The glomerular volume (VG), kidney-to-body weight ratio (KW/BW), urinary albumin excretion rate (UAER) and creatinine clearance (Ccr) were observed. The expression levels of transforming growth factor-beta1 (TGF-beta1), connective tissue growth factor (CTGF), fibronectin (FN) and plasminogen activator inhibitor-1 (PAI-1) were detected by real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) at the end of the experiment. RESULTS: UAER, Ccr, VG and KW/BW ratio were significantly higher in the untreated group than those in the normal control group (P<0.05). The expression levels of TGF-beta1, CTGF, PAI-1 and FN in the untreated group were also significantly higher as compared with those in the normal control group (P<0.05). UAER, Ccr, VG, KW/BW ratio and the levels of TGF-beta1, CTGF, PAI-1 and FN in the Salvia miltiorrhiza-treated group were obviously lower than those in the untreated group (P<0.05). CONCLUSION: Salvia miltiorrhiza can protect rats with streptozotocin diabetes from diabetic nephropathy by suppressing the over-expressions of TGF-beta1, CTGF, PAI-1 and FN in renal cortex.