Abstract: The Spontaneously Diabetic Torii (SDT) rat shows Impaired Glucose Tolerance (IGT) before the onset of diabetes. The present study investigated the effects of an improvement of IGT on the incidence of diabetes in male SDT rats. Voglibose, α-glucosidase inhibitor was used to improve glucose intolerance. In SDT rats at 10 weeks of age, a single dose of voglibose (0.03, 0.1 and 0.3 mg kg-1) improved the glucose tolerance dose-dependently. Moreover, voglibose was administered as a dietary mixture to SDT rats from 10-20 weeks of age. As a result, voglibose suppressed the incidence of diabetes in SDT rats. In voglibose-treated rats at 20 weeks of age, pancreatic weights were increased and the histopathological pancreatic changes such as irregular boundaries, atrophy, fibrosis and decrease of insulin-immunoreactivity in islets were improved. In conclusion, inhibition of postprandial hyperglycemia prevented the incidence of diabetes in SDT rats. Also, SDT rat is a useful model for development of a preventive drug on diabetes.