Objectives: This study was designed to evaluate the anti-diabetic effects of Spargaium stoloniferum Buchanan-Hamilton (Sparganii Rhizoma, SR) extract on diabetic rats. Methods: Diabetes was induced with Sprague-Dawley rats by high fat/high sucrose (HF/HS) diet for 4 weeks and injection of a single low dose of streptozotocin (STZ; 35 mg/kg). SR water extract at 500 mg/kg was orally administrated once a day for 4 weeks. Body weights, food and water intakes and urine volumes were measured. The levels of glucose, insulin, total cholesterol, glutamic oxaloacetic transaminase and glutamic-pyruvic transaminase (GPT) were measured in the sera of rats. Histological changes were observed in pancreas, liver, and kidney tissues by H&E staining. Results: The administration of Sparganii Rhizoma extract at 500 mg/kg in diabetic rats did not shown a significant difference in body weight changes and GPT levels, but showed meaningful changes in an increase of urination volume, and decrease of serum glucose and insulin levels. Total cholesterol and GPT levels were also significantly decreased after SR extract administration in diabetic rats. Furthermore, the abnormal changes of pancreas, liver and kidney were also improved by Sparganii Rhizoma extract administration. Conclusions: These results indicate that SR extract can improve HF/HS-diet and STZ-induced diabetic damages in rats through inhibition of the blood glucose and insulin increase.