Purpose: This study was conducted to identify emotional labor, nursing work environment, self-efficacy and happiness index and address factors associated with happiness index to provide basic resources for national psychiatric hospital nurses` happiness at work. Methods: Participants were 249 nurses working in 5 national psychiatric hospitals. They participated in the survey and data were collected from May 16 to July 30, 2016. Data were analysed using SPSS/WIN 22.0. Results: Mean scores were nurses` emotional labor, 3.89, nursing work environment, 2.77, self-efficacy, 3.77, and happiness index, 3.52. There were significant differences on the happiness index for: department, type of work, career length, position and payment. Happiness index was influenced by self-efficacy, work environment and emotional labor. Explanatory power of these variables was 36.9%. Conclusion: These results show that self-efficacy and work environment are important factors related to the happiness of the national psychiatric hospital nurses. Additionally, developing an effective program to facilitate self-efficacy of nurses and research studies to identify effects of such a program are required.