We herein describe a 59-year-old woman who had undergone a total gastrectomy for gastric carcinoma and suffered from postprandial hypoglycemia characterized by a loss of consciousness and spasms. She was diagnosed with reactive hypoglycemia and treated with nutrition therapy, but the frequency and severity of the hypoglycemic episodes did not decrease. She was subsequently treated successfully with miglitol, an alpha-glucosidase inhibitor (α-GI) taken twice a day; other α-GIs (acarbose and voglibose) were not effective. In conclusion, the administration of miglitol was effective for preventing reactive hypoglycemia secondary to late dumping syndrome.