Reactive hypoglycemia induced by late dumping syndrome is often observed after gastrectomy. However, no effective therapy has yet been fully established. We herein describe a case in which concurrent therapy with a low-carbohydrate diet using low-glycemic-index food and an alpha-glucosidase inhibitor, miglitol, very effectively ameliorated the postprandial fluctuations in the blood glucose and plasma insulin levels in a patient with reactive hypoglycemia due to late dumping syndrome following total gastrectomy. The administration of miglitol under a low-carbohydrate diet using low-glycemic-index food may therefore be an ideal treatment for reactive hypoglycemia due to late dumping syndrome.