The purpose of this study is to understand the effects of mental health, emotional intelligence, and occupational stress on work happiness of nurse's aides. In October 2019, a survey was conducted targeting total 227 nurse's aides working for long-term care hospitals and clinics. Using the IBM SPSS 25 Statistical Program, the collected data was analyzed through the t-test, ANOVA, Pearson's correlation coefficient, and multiple linear regression analysis. The results of this study are as follows. The factors affecting the work happiness of nurse's aides were occupational stress, mental health, and emotional intelligence, and the explanatory power was 64.5%. When the occupational stress was higher, and when the mental health was lower, the work happiness was not good. Thus, for the work happiness of nurse's aides, there should be some intervention programs that could reduce their occupational stress and also improve their mental health. Also, when selecting the subjects of programs, it would be necessary to consider the degree of emotional intelligence and resilience of nurse's aides.