TGP, extracted from the traditional Chinese herb root of Paeonia lactiflora pall, has been shown to have therapeutic effect in experimental diabetic nephropathy. However, its mechanism is not fully understood. In this study, the effects of TGP on oxidative stress were investigated in the kidney of diabetic rats induced by streptozotocin. TGP (50, 100, 200mg/kg) was orally administered once a day for 8 weeks. TGP treatment in all three doses significantly lowered 24 h urinary albumin excretion rate in diabetic rats and attenuated glomerular volume. TGP treatment with 100 and 200mg/kg significantly reduced indices for tubulointerstitial injury in diabetic rats. The level of MDA was significantly increased in the kidney of diabetic rats and attenuated by TGP treatment at the dose of 200mg/kg. TGP treatment in a dose-dependent manner decreased the level of 3-NT protein of the kidney which increased under diabetes. T-AOC was significantly reduced in diabetic rat kidney and remarkably increased by TGP treatment at the dose of 100 and 200mg/kg. Activity of antioxidant enzyme such as SOD, CAT was markedly elevated by TGP treatment with 200mg/kg. Western blot analysis showed that p-p38 MAPK and NF-kappaB p65 protein expression increased in diabetic rat kidney, which were significantly decreased by TGP treatment. It seems likely that oxidative stress is increased in the diabetic rat kidneys, while TGP can prevent diabetes-associated renal damage against oxidative stress.