The present study was undertaken to see the possibility of production of spontaneous diabetes rat by repeating the selective breeding of normal rats with a slight impairment of glucose tolerance. One hundred and thirty male and 81 female normal rats of Wistar strain were obtained from an experimental animal farm as foundation stock and 9 male and 9 female rats were chosen as breeding stock by oral glucose tolerance test. By the crossing, 89 male and 73 female rats were obtained (F₁). The mean glucose tolerance curve of these offsprings was significantly higher than that of the foundation stock. Twelve male and 13 female rats were chosen among the F₁ rats as breeding stock by glucose tolerance test. The crossing of them yielded 116 male and 88 female rats (F₂). The mean glucose tolerance curve of F₂ was significantly higher than that of F₁ and some of them had a diabetic test and a positive test for urine sugar during the test. The result demonstrated the possibility of production of spontaneous diabetes from normal rats by the selective breeding.