Objective The present study aimed to report the initial seizure threshold (IST) of a brief-pulse bilateral electroconvulsive therapy (BPBL ECT) in Korean patients with schizophrenia/schizoaffective disorder and to identify IST predictors. Methods Among 67 patients who received ECT and diagnosed with schizophrenia/schizoaffective disorder based on the criteria of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, we included 56 patients who received 1-millisecond BP-BL ECT after anesthesia with sodium thiopental between March 2012 and June 2018. Demographic and clinical information was gathered from electronic medical records, and a multiple regression analysis was conducted to identify predictors of the IST. Results The mean age of the patients was 36.9±12.0 years and 30 (53.6%) patients were male. The mean and median IST were 105.9±54.5 and 96 millicoulombs (mC), respectively. The IST was predicted by age, gender, and dose (mg/kg) of sodium thiopental. Other physical and clinical variables were not associated with the IST. Conclusion The present study demonstrated that the IST of 1-ms BP-BL ECT following sodium thiopental anesthesia in Korean patients was comparable to those reported in previous literature. The IST was associated with age, gender, and dose of sodium thiopental.