Compassion competence is a core nursing skill that is significant in understanding and alleviating the physical and mental distress of individuals. Self-leadership and nursing professional values are also reported as important factors in improving the clinical care practices of nurses and may have a positive effect on improving the compassion competence of nurses. However, there are few studies examining the relationship between these variables in community mental health nurses. This study investigated the mediating effect of professional values on the relationship between self-leadership and compassion competence of community mental health nurses. A cross-sectional correlational study was conducted with 121 community mental health nurses from 30 mental health welfare centers in South Korea. Participants completed self-report scales on self-leadership, nursing professional values, and compassion competence. Baron and Kenny's regression method and the Sobel test revealed significant mediating effects of nursing professional values on the relationship between self-leadership and compassion competence. Participants' mean compassion competence scores were 3.57 (SD = 0.45) on a 5-point scale. Compassion competence positively correlated with self-leadership (r = 0.67, P < .001) and nursing professional values (r = 0.60, P < .001). Nursing professional values played a partial mediating role in the relationship between self-leadership and compassion competence (Z = 3.23, P = .001). Compassion competence of community mental health nurses can be improved by promoting self-leadership and nursing professional values.