Introduction: Blonanserin is a relatively new atypical antipsychotic drug, and has been used in Korea and Japan for 1 and 3 years, respectively. Therefore, the clinical characteristics of blonanserin remain unclear. In this study, to clarify the features of blonanserin, we performed prospective and long- term comparative investigations of patients treated with blonanserin. Methods: We followed 10 psychiatric patients who were switched to blonanserin from other antipsychotics for 1 year (schizophrenia: 8; mental retardation: 2). In the light of quality of life, we focused on adverse effects of patients during the follow- up. Results: In the long- term follow- up, (i) hyperprolactinemia is more frequently in risperidone than in blonanserin; however, it is more often in blonanserin than in olanzapine; and (ii) weight gain is more common in olanzapine than in blonanserin. Discussion: We switched to blonanserin from other antipsychotic drugs within the same case, and then followed the case for 1 year. We consider that long- term observations within the same case lead to obvious comparisons among drugs. On the basis of our findings, we conclude that blonanserin may be useful for the maintenance treatment of schizophrenia without inducing hyperprolactinemia and weight gain.