This study developed an ethical practice self-efficacy scale for counselors (EPSES-C). Additionally, it reviewed the validity of the developed scale based on the responses of a group of school counselors to examine the possibility of practically applying this scale in schools. Specifically, it investigated previous studies and ethical guidelines regarding the ethics of counselors to complete the development of the scale based on 27 items. It obtained data of 244 counselors working in elementary, middle, and high schools as well as in the Offices of Education in South Korea. Moreover, it conducted an exploratory factor analysis by dividing samples randomly and using data of 122 counselors, in addition to performing a confirmatory factor analysis based on the data of the remaining 122 counselors. The final scale included 15 items based on the results of the analyses, and the study ensured this scale’s validity and reliability. Additionally, the study derived five sub-factors, including self-efficacy related to respect for rights of counselees, the understanding of ethics of counseling, the prevention of suicide of counselees, the development of expertise, and ensuring counselee confidentiality. The analysis results indicated that counselors who had a higher EPSES-C score tended to be less prone to exhaustion. They were also likely to make more ethical judgments in difficult situations during practical counseling in schools. Based on these results, criterion validity was ensured. Reliability ranged from .69 to .79 with respect to the sub-factors, and as the reliability of all items was calculated to be .90, this study verified the possibility of the developed scale being effectively applied in schools.