Postprandial glucagon secretion was shown to be dysregulated in patients with type 2 diabetes. However, the differences in secretory patterns between obese and non-obese patients and their physiological effects on plasma glucose levels are not fully understood. This study population consisted of 21 (10 obese and 11 non-obese) consecutive patients with type 2 diabetes admitted for glycemic control. A 3-hour mixed-meal tolerance test was performed after glycemic control improved. Six non-diabetic subjects were also enrolled in the test. Postprandial glucagon levels increased after 30 min in diabetic patients but not in non-diabetic subjects. The glucagon levels in obese diabetic patients were significantly higher than those in non-obese diabetic patients, while the percent values of postprandial glucagon levels were not different between these groups. In diabetic patients, there were significant positive correlations between the percent value at 30 min and the early postprandial glucose levels at 0, 15 and 30 min and the areas under the curve (AUC0-30 and AUC30-90). Interestingly, the ratio of this percent glucagon value to the C-peptide level at 30 min was significantly associated with the late half of the postprandial glucose levels at 90, 120, 150 and 180 min and the AUC90-180. This is the first report that demonstrates the glucagon secretory patterns and the close correlations in detailed time course between the early postprandial glucagon response and the early and the late half of the postprandial glucose levels in obese and non-obese patients with type 2 diabetes.