Background: Chronic inflammation plays an important role in the progression of diabetic nephropathy (DN) and that the infiltration of macrophages in glomerulus has been implicated in the development of glomerular injury. We hypothesized that the plant polyphenolic compound curcumin, which is known to exert potent anti-inflammatory effect, would ameliorate macrophage infiltration in streptozotocin (STZ)-induced diabetic rats. Methods. Diabetes was induced with STZ (55 mg/kg) by intraperitoneal injection in rats. Three weeks after STZ injection, rats were divided into three groups, namely, control, diabetic, and diabetic treated with curcumin at 100 mg/kg/day, p.o., for 8 weeks. The rats were sacrificed 11 weeks after induction of diabetes. The excised kidney was used to assess macrophage infiltration and expression of various inflammatory markers. Results: At 11 weeks after STZ injection, diabetic rats exhibited renal dysfunction, as evidenced by reduced creatinine clearance, increased blood glucose, blood urea nitrogen and proteinuria, along with marked reduction in the body weight. All of these abnormalities were significantly reversed by curcumin. Hyperglycemia induced the degradation of IB and NF-B activation and as a result increased infiltration of macrophages (52%) as well as increased proinflammatory cytokines: TNF- and IL-1. Curcumin treatment significantly reduced macrophage infiltration in the kidneys of diabetic rats, suppressed the expression of above proinflammatory cytokines and degradation of IB. In addition, curcumin treatment also markedly decreased ICAM-1, MCP-1 and TGF- 1protein expression. Moreover, at nuclear level curcumin inhibited the NF-B activity. Conclusion: Our results suggested that curcumin treatment protect against the development of DN in rats by reducing macrophage infiltration through the inhibition of NF-B activation in STZ-induced diabetic rats.