E. japonica is a well-known medicinal plant in Japan. The leaves of E. japonica were reported to have a hypoglycemic action. However, seeds of E. japonica are discarded and not used. To elucidate for anti-diabetic effects of E. japonica, Type 2 diabetic mice were allocated to control group, E. japonica leaf, and seed extract group. Animals were fed a 2018S Teklad global 18% protein rodent diet. Animals were received daily oral injections of E. japonica leaf or seed extract at a dose of 200 mg/kg body weight for 6 weeks. Body weight, food intake and water intake, and total adipose tissue weight of animals were significantly reduced by feeding of E. japonica leaf extract. All E. japonica extract groups significantly decreased fasting blood glucose, glycosylated hemoglobin levels, size of adipocytes and serum adiponectins. However, they did not have a beneficial effect on the serum triglyceride and cholesterol in the diabetic animals. These results suggest that E. japonica seed and leaf extracts have a antidiabetic effect by controlling of blood glucose and decrease of size of adipocytes in db/db mice and seed extract is more effective in hypoglycemic action than leaf extract.