This study investigated the antidiabetic effect of amaranth grain ethanol extract (AEE) in a diabetic animal model, db/db mouse. The mice were divided into 4 groups: normal control mice (C57BL/6J), diabetic mice (C57BL/6J db/db), diabetic mice fed a lower concentration of AEE (0.3 mg/kg), and diabetic mice fed a higher concentration of AEE (0.5 mg/kg). After 10 weeks of treatment, body weights, blood insulin levels and blood glucose levels of each group were compared. At the end of treatment, the results showed that both AEE supplemented groups had lower body weights than those in the diabetic groups although higher than those in the normal groups. Moreover, in both AEE supplemented groups, serum insulin levels were higher and blood glucose levels were lower than those in the diabetic groups although both values were higher than those in the normal groups. The results of this study suggest that AEE can alleviate many of the common symptoms of diabetes in diabetic mice and, therefore, has potential as a therapeutic supplement for normalization of blood glucose and insulin levels in humans.