To determine whether miglitol administration improves glycemic control and reduces the frequency of hypoglycemia in type 1 diabetes mellitus (T1DM) patients treated with intensive insulin therapy, we analyzed the effect of miglitol on daily insulin doses, body weight, hypoglycemia, and incretin hormone responses during meal tolerance tests (MTT). Eleven T1DM subjects (21-77 years) undergoing intensive insulin therapy, took 25 mg (weeks 0-4) and 50 mg miglitol (weeks 4-12) thrice daily, immediately before meals. At weeks 0 and 12, 9 of 11 subjects underwent MTT. In present study, mean HbA1c, glycoalbumin, and 1,5-anhydroglucitol levels were significantly improved. The blood glucose level 1 h after dinner was significantly lower at week 12 than at week 0 (p = 0.008). From week 0 to 12, there was a significant decrease in the body mass index (BMI; p = 0.0051), frequency of preprandial hypoglycemic events (p = 0.012), and daily bolus insulin dosage (p = 0.018). The change in active glucagon-like peptide-1 (GLP-1) at 120 min significantly increased at week 12 (p = 0.015). The change in total glucose-dependent insulinotropic peptide (GIP) significantly decreased in the MTT at week 12. These results demonstrate that addition of miglitol on intensive insulin therapy in T1DM patients has beneficial effects on reducing BMI, bolus and total insulin dosage, and frequency of preprandial hypoglycemic events. MTT findings suggest that this combination therapy improves blood glucose control by delaying carbohydrate absorption and modifying the responses of incretins, GIP, and GLP-1.