Objectives : To investigate the therapeutic effect and underlying mechanisms of rhein on renal fibrosis in diabetic rats. Methods : Diabetic nephropathy (DN) was induced in adult Wistar rats via introperitoneal injection of streptozotocin (STZ) (20 mg/kg/d) for three consecutive days. Two days after the last dose of STZ, rhein was administered to the diabetic rats at a dose of 25 mg/kg or 50 mg/kg, twice a day by gavage, respectively. Following 28 days treatment with rhein, the plasma glucose and creatinine levels were measured, the renal levels of TGF-${eta}1$ protein and mRNA were examined, and the fibronectin mRNA levels were also determined. Results : Rhein significantly inhibited the increased plasma glucose and creatinine levels of diabetic rats in a dose- and a time-dependent way. Immunohistochemical analysis showed both doses of rhein markedly attenuated elevated induction of renal TGF-${eta}1$ protein expressions in diabetic rats. Additionally, the high dose of rhein improved both TGF-${eta}1$ and fibronectin mRNA expressions, while the low dose of rhein only alleviated fibronectin mRNA expressions. Conclusions : Rhein can improve renal fibrosis in diabetic nephropathy rats, and which may be mediated through inhibition of the renal mRNA expressions of TGF-${eta}1$ and fibronectin.