Diabetic nephropathy is characterized by progressive loss of renal function, persistent proteinuria, and relentless accumulation of extracellular matrix leading to glomerulosclerosis and interstitial fibrosis. This study investigated the potential effects of long-term expression of exogenous hepatocyte growth factor (HGF) on normal and diabetic kidneys. Intravenous injection of human HGF gene via naked plasmid vector resulted in abundant HGF protein specifically localized in renal glomeruli, despite an extremely low level of transgene mRNA in the kidney. In uninephrectomized mice made diabetic with streptozotocin, delivery of exogenous HGF gene ameliorated the progression of diabetic nephropathy. HGF attenuated urine albumin and total protein excretion in diabetic mice. Exogenous HGF also mitigated glomerular mesangial expansion, reduced fibronectin and type I collagen deposition, and prevented interstitial myofibroblast activation. In addition, HGF prevented kidney cells from apoptotic death in the glomeruli and tubulointerstitium. Moreover, expression of HGF inhibited renal expression of TGF-beta1 and reduced urine level of TGF-beta1 protein. Therefore, despite the effects of HGF on diabetic nephropathy being controversial, these observations suggest that supplementation of HGF is beneficial in ameliorating diabetic renal insufficiency in mice.