Objective : The purpose of this study was to investigate diagnostic groups, interventions, and standardized assessments in mental health in occupational therapy through a systematic review. Methods : The systematic review was executed using PubMed, Springer Link, Wiley Journal, and Science Direct. The key words used for the search were “occupational therapy”, “mental health”, “psychiatric”, “mental illness”. Thirteen studies were used for the data analysis, and the levels of evidence were levels Ⅰ, Ⅱ, Ⅲ, and Ⅴ. Results : 1. The subjects suffered from dementia(30.8%), schizophrenia(15.4%), panic disorders(7.7%), and depression(7.7%). 2. The methods used were client-centered intervention(46.2%), work and education(23.1%), Activities of Daily Living(ADL) training(15.3%), neurocognitive training(15.3%), and environment and context intervention(7.7%). With the exception of environment and context intervention, all interventions have positive effects on the mental illness of the patients. 3. The areas of standardized assessments were health & wellness(41.3%), occupational performance(28.3%), quality of life(19.6%), role competence(8.7%), and participation(2.1%). Conclusion : This systematic review provides evidence concerning the effectiveness of occupational therapy in mental health. Studies on effective intervention to facilitate community participation for various diagnostic groups have to be conducted. In addition, the effects on occupational therapy in mental health should be assessed from multilateral perspectives.