Mosapride citrate (Mc) is one of 5-HT4-receptor agonists, and has a pharmacological action to promote physiological gastrointestinal peristalsis. This manuscript showed that Mc from the start of treatment was useful for functional constipation (FC) to satisfy Rome Ⅳ criteria in three infants including one male, mean age: 4 years old.All patients revealed Bristol Stool Form Scale (BSFS) 1, and one case complicated paradoxical diarrhea. Two patients had lost the spontaneous defecation, and completely depended on glycerin enema.Mc 0.29 mg/kg/day with magnesium oxide or lactulose added to probiotics was administered to the patients, who obtained the spontaneous defecation over once a day and BSFS 4 or 5 in the treatment period for five months.