The existence of multiple serotonin (5-HT) receptor subtypes has been proposed based on radioligand binding assay technique and other functional assay. Recent advance of neuropsychopharmacology has contributed to elucidating their physiological functions, ranging from molecular biological to clinical characteristics. Abnormalities of central 5-HT function are currently thought to play a significant role in mental disorders such as affective disorder, anxiety disorder, eating disorder and negative symptoms of schizophrenia, and in the regulation of physical functions such as body temperature, blood pressure and pain. The most significant outcome of the basic pharmacological work has been successful application of 5-HT receptor agents to the treatment of the above clinical disorders. In this article, the authors review the history of 5-HT receptor research and the role of 5-HT receptor in clinical disorders.