Schizophrenia is a psychiatric disease which requires a long term treatment. Thus, patient's therapeutic compliance can be very crucial to the disease's prognosis. Moreover, the adverse effects of drugs are also important to determine the patient's therapeutic compliance. The atypical antipsychotic drugs have been improved in the way to strengthen therapeutic effects and to reduce adverse effects. Blonanserin, an atypical antipsychotic, is a selective serotonin-dopamine agonist which blocks the dopamine D2/D3 receptors and serotonin 5-HT2A receptor. Blonanserin is well known to include parkinsonism, akathisia and insomnia. In this case report, Blonanserin treatment was given to patients who admitted to the closed ward due to psychotic symptoms such as idea of reference, persecutory delusion, auditory hallucination and blunted affect. The patients showed manic symptoms including elated mood, talkativeness, hyperactivity after the increase of Blonanserin dose up to 24 mg. Such manic symptoms were improved after Blonanserin dose was decreased to 16 mg. Many researches have reported newly-evoked manic/hypomanic episodes in schizophrenic patients after the use of atypical antipsychotics such as Risperidone, Olanzapine and Ziprasidone. However, there is no report of Blonanserin-induced manic/hypomanic episode. Therefore, further study is necessary to evaluate the manic/hypomanic episodes which are thought to be the adverse effects of Blonanserin.