The purpose of this study is to develop the core competencies of social service corps working in social welfare facilities, in order to contribute to the enhancement of their work performance and the qualitative improvement of services they provide. To achieve this objective, a mixed methods research approach was employed, involving a survey conducted on 378 social service corps working in social welfare facilities and in-depth interviews with 11 administrative workers responsible for overseeing social service corps. In the first phase, a quantitative study was conducted targeting social service corps working in social welfare facilities nationwide. The study involved the utilization of an interval estimation method that incorporated the requirements demanded by institutions and competencies, and as a result, a total of 13 core competencies were identified. Specifically, 3 competencies were identified within the domain of ‘Disposition and Attitude,’ 6 competencies were identified within the domain of ‘Social Welfare Practice Competencies,’ and finally, 4 competencies were identified within the domain of ‘Job Performance Competencies.’ Subsequently, during the second phase of the qualitative study, the researchers conducted Focus Group Interviews with 11 administrative workers responsible for managing social service corps duties in social welfare facilities. Core competencies were extracted through thematic analysis based on the duties and changing work environment of the social service corps. The results revealed 3 competencies under ‘Cultivated Literacy and Attitude,’ 5 competencies within ‘Social Welfare Practice Competencies,’ and 7 competencies within ‘Job Performance Competencies.’ The significance of this study lies in its comprehensive presentation of outcomes through the incorporation of both quantitative and qualitative methods, involving not only the social service corps that participated in training but also the administrative personnel that supports the performance of social service corps and utilization of the competencies. This study holds valuable implications as fundamental material for the advancement of the training and education system for the social service corps.