Irritable bowel syndrome is a functional gastrointestinal disorder characterized by abnormal sensation and motility in the lower gastrointestinal tract. In constipation-type irritable bowel syndrome, decreased bowel motility causes stagnation of feces and gas, resulting in enhanced pain sensation of the bowel. Mosapride citrate is a selective serotonin 5- HT4 receptor agonist and enhances propulsive activity throughout the gastrointestinal tract. Mosapride citrate was orally administered to 11 patients with constipation-type irritable bowel syndrome to investigate its effect on this disease. The result showed that mosapride citrate alleviated abdominal pain and abdominal distension, loosened stools, shortened bowel transit time, and decreased flatus in the bowel. The results suggest that mosapride citrate is useful for the treatment of irritable bowel syndrome.