Present study was carried out to examine effects of nanopowdered chitosan on antidiabetic activity in db/db mice. Twenty-eight 8-week-old mice were divided into 4 groups: (1) control, nondiabetic control mice; (2) group 1, diabetic control mice with not treated chitosans; (3) group 2, diabetic mice given 2% powdered chitosan; and (4) group 3, diabetic mice given 2% nanopowdered chitosan. The serum glucose in group 3 reduced by 56%, as compared to group 2 (28%). The total serum cholesterol in group 3 decreased by 31.6%, while group 2 reduced by 18.2%. Triglyceride was decreased by 33.6% in group 3 and by 22.5% in group 2. The insulin of group 2 and 3 were significantly increased by 51.7 and 92.9%, respectively. Only group 3 was recovered from the ${eta}$-cell destruction. Based on the result of the study, it is suggested that nanopowdered chitosan has higher antidiabetic activities than powdered.