Objectives The response of schizophrenia or schizoaffective disorder patients to antipsychotics remains insufficient. Therefore, augmentation with additional antipsychotics is common in clinical practice. This study examined the efficacy and safety of amisulpride augmentation in schizophrenia patients partially responsive to antipsychotics. Methods Twenty-nine schizophrenia or schizoaffective disorder patients without treatment response to antipsychotics monotherapy were included in this study. Psychotic symptoms were evaluated using Brief Psychiatry Rating Scale (BPRS), Clinical Global Impression-Severity (CGI-S), and Clinical Global Impression-Improvement (CGI-I). The side effects were evaluated using Barnes Akathisia Rating Scale (BARS) and Simpson-Angus Scale (SAS) at baseline, 4 weeks, 8 weeks, and 12 weeks after the amisulpride augmentation. Results Among the 29 patients, 28 completed the study. At week 12, the mean BPRS score (p<0.001) and CGI-S score (p=0.002) showed significant improvement compared to the baseline. There was no increase in extrapyramidal symptoms according to SAS (p=0.090) and BARS (p=0.137) after the amisulpride augmentation. Conclusion This study demonstrated the efficacy and safety of amisulpride augmentation in schizophrenia or schizoaffective disorder patients partially responsive to antipsychotics. Further studies investigating the efficacy of amisulpride augmentation therapy using placebo control are necessary to confirm the results.