A novel cinnoline derivative having an antagonistic activity against serotonin 5-HT.sub.3 receptor, its pharmaceutically acceptable salts, its N-oxide derivatives or solvates thereof, and pharmaceutical formulations containing the same for the prevention and/or treatment of various disorders such as nausea and/or emesis caused by anticancer drugs or X-ray treatment, central nervous disorders such as anxiety and/or neuropathy, gastroenteric diseases such as indigestion, chronic gastritis, digestive ulcer, irritable bowel syndromes and the like, hemicrania, cluster headache, trigeminal neuralgia, arrhythmia and the like.