We previously reported that pyridoxine and its derivatives exert antidiabetic effects by alleviating postprandial hyperglycemia via inhibition of carbohydrate-hydrolyzing enzymes in normal sprague–dawley (SD) rats. In this study, we aimed to further evaluate whether long-term pyridoxal supplementation decreases the blood glucose levels using SD rats. SD rats were randomly assigned to groups fed a high-carbohydrate diet (66.1% cornstarch) with or without pyridoxal (4%) for 36 days. Changes in body weight, blood glucose levels, and food intake were measured daily for 36 days. Dietary supplementation with pyridoxal significantly decreased the blood glucose levels (P<0.001) and body weight (P<0.001) in mice. Glycated hemoglobin (HbA1c) levels, which are good indicators of plasma glucose concentrations over prolonged periods, were also significantly decreased over five weeks (P<0.001). Similarly, dietary treatment with Acarbose ® (0.04%), a positive control, also significantly decreased the blood glucose and HbA1c levels and body weight. Overall, our findings suggest that pyridoxal inhibits weight gain and alleviates postprandial hyperglycemia by decreasing glucose absorption and HbA1c levels.