Objectives: The aim of the study was to examine the relationship between workplace bullying, mental health and an intention to leave among nurses, and the mediating role of self-efficacy. Material and Methods: This cross-sectional study was conducted among 385 nurses in Taiwan. Data were collected by means of self-report questionnaires, including the Negative Acts Questionnaire-Revised, the General Self-Efficacy Scale, the Chinese Health Questionnaire, and the Employee’s Turnover Intentions and Job Destination Choices Scale. Descriptive statistics, Pearson’s correlation and hierarchical regression analyses were used. Results: Bullying was found to negatively correlate with self-efficacy and mental health, and positively with an intention to leave. Self-efficacy positively correlated with mental health, and negatively with an intention to leave. Hierarchical regression showed that bullying and self-efficacy were significant predictors of both mental health and an intention to leave. Self-efficacy partially mediated the relationship between bullying and mental health, as well as an intention to leave. Conclusions: Self-efficacy acted as a mediator of workplace bullying, mental health and an intention to leave among nurses. It could protect victims from the devastating effects of bullying behaviors. Int J Occup Med Environ Health. 2019;32(2):245–54