Remedies effective for the improvement of colonic motor dysfunction such as irritable bowel syndrome, constipation or intestinal atony without causing side effects on the central nerve system. These colonic motor dysfunction remedies comprise, as active ingredients, aminothiazole derivatives represented by the following formula (I) or a salt or hydrate thereof: wherein R1, R2 and R3 may be the same or different and each independently represent a hydrogen atom or a hydroxyl, lower alkyl, lower alkoxy, amino, nitro or cyano group, R4 and R5 may be the same or different and each independently represent a hydrogen atom or a lower alkyl group, and n stands for an integer of from 2 to 4.