Miglitol, a pseudomonosaccharide alpha-glucosidase inhibitor (alphaGI), was more effective at reducing blood glucose levels at 30 and 60 min after a meal than voglibose. Speculating that miglitol administered even after the start of a meal may be effective, we evaluated the timing of administration of miglitol on the plasma glucose and serum insulin levels in 13 type 2 diabetic patients. Miglitol was administered in four different intake manners in each patient (control: no miglitol; intake 1: just before breakfast; intake 2: 15 min after the beginning of breakfast; intake 3: 30 min after the beginning of breakfast). The area under the curve (AUC) of plasma glucose was significantly decreased under all the intake conditions, as compared with the AUC in the control. The AUC of serum insulin tended to be lower in all the three groups than in the control, although the differences were not statistically significant. Thus, miglitol administered anytime within 30 min after the start of a meal is effective for glycemic control. These results suggest that if patients miss taking miglitol at the beginning of a meal, they can still take the drug until 30 min after starting their meal.