A 53-year-old man with chronic, refractory schizophrenia was hospitalized because of his symptoms of hostility, aggression, insomnia, delusions, and auditory hallucinations, despite his medication with clozapine 200 mg per day. His initial laboratory studies revealed no remarkable findings. Clozapine was titrated to 350 mg per day for marked psychotic symptoms, but it seemed to be only slightly effective. Meanwhile, he complained of salivation worsening and wanted to discontinue clozapine treatment because of this adverse effect. We then added amisulpride 600 mg per day for augmentation of clozapine. Interestingly, there was a significant improvement in his auditory hallucinations, delusions, conceptual disorganization, and on the positive and negative syndrome scale (PANSS). Also, the adverse effect of sialorrhea was improved during the following days and nights.