Lycium barbarum, extensively utilized as a medicinal plant in China for years, exhibits antitumor, immunoregulative, hepatoprotective, and neuroprotective properties. The present study aims to investigate the hyperglycemic and antidiabetic nephritic effects of polysaccharide which is separated from Lycium barbarum (LBPS) in high-fat diet-streptozotocin- (STZ-) induced rat models. The reduced bodyweight and enhanced blood glucose concentration in serum were observed in diabetic rats, and they were significantly normalized to the healthy level by 100 mg/kg of metformin (Met) and LBPS at doses of 100, 250, and 500 mg/kg. LBPS inhibited albuminuria and blood urea nitrogen concentration and serum levels of inflammatory factors including IL-2, IL-6, TNF-α, IFN-α, MCP-1, and ICAM-1 compared with diabetic rats, and it indicates the protection on renal damage. Furthermore, the activities of SOD and GSH-Px in serum were enhanced strikingly by LBPS which suggests its antioxidation effects. LBPS, compared with nontreated diabetic rats, inhibited the expression of phosphor-nuclear factors kappa B (NF-κB) and inhibitor kappa B alpha in kidney tissues. Collectively, LBPS possesses antidiabetic and antinephritic effects related to NF-κB-mediated antioxidant and antiinflammatory activities.