A therapeutic method and pharmaceutical compositions for treatment of irritable bowel syndrome including non-constipated irritable bowel syndrome such as diarrhea-predominant irritable bowel syndrome and alternating constipation/diarrhea irritable bowel syndrome in male and female patients, which may comprise administering a patient with from 0.001 to 0.05 mg of ramosetron hydrochloride as a daily dose or an equivalent molar amount of ramosetron or its pharmaceutically acceptable other salt.