With the increasing popularity of group counseling, it becomes imperative to comprehend the development of group relational structures between leaders and members. However, due to the scarcity of research on the interaction analysis of group dynamics, this case study aimed to examine the relational structure of an unstructured counseling group using social network analysis. From seven unstructured counseling groups, the case study selected the one with the best performance based on the participants’ score changes on the Adult Mental Health Scale. Through visual analysis, significant changes in the interaction structures between group leaders and two types of members were revealed. Additionally, mathematical analysis yielded patterns in the number of themes, counts of self-disclosure actions, and levels of interaction intensity. Both qualitative and quantitative findings implicitly reflected changes in group cohesion throughout the various process stages. As a result, this study offers practical implications for training group leaders on different group process issues, including the transition of authority and members’ roles and functions at various group stages. Furthermore, the research provides valuable insights for the future exploration of counseling groups.