Objective In type 2 diabetic mellitus, diabetic nephropathy is the most common and a serious complication to lead the cause of mortality and morbidity. It is important that diabetic mellitus patients can be delayed for a long time into progressive diabetic nephropathy. In this study, we investigated whether curcumin could ameliorate diabetic nephropathy or not. Methods At 25 weeks, we divided into three groups: LETO rats (CON), OLETF rats for diabetic control (DM) and curcumin-treated (100 mg/kg/day) OLETF rats (CUR + DM). At 45 weeks, we measured body, kidney and epididymal fat weights. We collected 24 hours urine sample for the assessment of albumin, creatinine, MCP-1, SOD and MDA. Plasma insulin, adiponectin, total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), and triglyceride (TG) were measured. To identify insulin resistance, we calculated using IPGTT, Kitt, HOMA-IR, and HOMA-beta. To confirm the damage of renal cortex, we measured glomerular basement membrane (GBM) thickness, slit pore density, MCP-1, VEGF, TGF-β1, collagen type IV, and nephrin in vivo and in vitro. Results did not affect glucose control and insulin resistance. However it down-regulated serum lipid and also increased urine SOD level and plasma adiponectin level to epididymal fat/body weight ratio compared to OLETF rats. Additionally, it reduced albuminuria and GBM thickness with the restoration of slit pore density. In vitro study showed that it ameliorates nephrin whereas reduces inflammatory parameters such as ROS, MCP-1, VEGF, and TGF-β1 in high glucose induced podocyte cell lines, even though they did not show significant effects in vivo. Conclusion We suggest that curcumin ameliorates diabetic nephropathy through the improved anti-lipid and anti-inflammatory effects.