Study objectivesThe coronavirus disease 2019 (COVID-19) pandemic has resulted in major disruption to regular learning and training for medical staff. The aim of this study was to compare the learning efficacy between on-site training before the COVID-19 pandemic and online training during the pandemic for nurses, psychologists, social workers, and occupational therapists from Southeast Asia. MethodThe current study derived data from the International Mental Health Training Center Taiwan (IMHTCT) from 2018 to 2020. IMHTCT Trainees Learning Effect Questionnaire (ITLEQ) scores of the medical staff and demographic variables were collected. Reliability and validity of the ITLEQ were estimated. The independent t-test was used to compare differences in ITLEQ scores between the pre-training and post-training stages among the trainees. In addition, generalized estimating equations were used to estimate the predictive effect of online training on changes in ITLEQ scores over time. FindingsA total of 190 trainees were enrolled, including 92 social workers, 16 occupation therapists, 24 psychologists, and 58 nurses. The reliability and validity were satisfactory. The efficacy of the training programs at IMHTCT was significant for all of the healthcare workers. Furthermore, better training efficacy was found in the social workers and occupational therapists who received online training compared to those who received on-site training. The potential efficacy of online training was found in the nurses. ConclusionOur results demonstrate the importance of online training for mental healthcare workers during the COVID-19 pandemic. Online training may be implemented into regular training courses in the future.