The abilities of instant gruel manufactured with colored barley and oats to improve diabetic conditions were investigated using diabetes-induced mice and rats. Mice or rats were divided into a diabetic control group and one experimental group (seven animals per group). The control groups were fed without instant gruel and experimental groups were fed basal diets supplemented with 10% instant gruel for 8 weeks. The streptozotocin (STZ)-induced diabetic rats experimental group showed a significant decrease in food intake compared to the control group. Both Type Ⅱ diabetic mice and STZ-induced diabetic rats experimental groups showed higher increases in body weight than the control groups. The blood glucose levels of the experimental groups (352±12.2 mg/dL in Type Ⅱ diabetic mice; 296.4±13.2 mg/dL in STZ-induced diabetic rats) were lower than the untreated control groups (426.0±15.4 mg/dL in Type Ⅱ diabetic mice; 514.0±17.6 mg/dL in STZ-induced diabetic rats). The serum insulin levels of Type Ⅱ diabetic mice increased by 38.3% in the experimental group (12.8±1.1 ng/mL) compared to the control group (7.9±0.5 ng/mL). The immunohistochemical density of insulin-secreting cells and glucagon-like peptide-1 (GLP-1)-secreting cells in the pancreas were significantly higher in the experimental groups than the control groups for Type Ⅱ diabetic mice and STZ-induced diabetic rats. Therefore, we conclude that instant gruel manufactured with colored barley and oats stimulates the secretion of insulin and decreases blood sugar by activating insulin-secreting cells in the pancreatic islets of diabetic animals.