Mosapride citrate, a selective agonist of the 5-hydroxytryptaine (5-HT)₄ receptor, is typically used to treat heartburn, nausea, and vomiting associated with chronic gastritis or to prepare for a barium enema X-ray examination. Mosapride citrate reportedly improves insulin sensitivity in patients with type 2 diabetes. As mosapride citrate activates the motility of the gastrointestinal tract, we hypothesized that mosapride citrate affects incretin secretion. We examined the effect of the administration of mosapride citrate on the plasma glucose, serum insulin, plasma glucagon, and plasma incretin levels before breakfast and at 60, 120, and 180 min after breakfast in men with normal glucose tolerance (NGT) or impaired glucose tolerance (IGT) to exclude gastropathy. Mosapride citrate was administered according to two different intake schedules (C: control (no drug), M: mosapride citrate 20 mg) in each of the subject groups. The area under the curve (AUC) of the plasma glucose levels was smaller in the M group than in the C group. The time profiles for the serum insulin levels at 60 and 120 min after treatment with mosapride citrate tended to be higher, although the difference was not statistically significant. The AUCs of the plasma active and total glucagon-like peptide-1 (GLP-1) levels were significantly larger in the M group than in the C group. No significant difference in the AUC of the plasma glucose-dependent insulinotropic polypeptide (GIP) level was observed between the two groups. Our results suggest that mosapride citrate may have an antidiabetic effect by increasing GLP-1 secretion.