In this study, we investigated the counseling trainees’ first group counseling co-leader experiences. For this, we interviewed two graduate students who managed the Gestalt group counseling session as co-leaders. Interview data, transcripts of 10 session group counseling, 13 session supervision reports, and reflection journal of research participants were analysed by narrative method. The results were as follows. The research participants experienced anxiety due to lack of self-confidence at the early stage of the group, tension due to the double relationship with supervisor and professor, the colleagues and group members, and collaboration among co-leaders. As the group sessions and supervision based on the Gestalt theory continued, they were able to recover self-confidence through theoretical learning, technique exercises, watching Pearls’ video, and active cooperation of group members. Over time, they gradually applied various techniques autonomously with ongoing supervision, and experienced group cohesion and willingness to resolve problems through brave self-exposures of several group members. In the process, cooperation between collaboration leaders has also been experienced, and positive experiences have been experienced in which the tension caused by the double relationship changes into deep trust. Finally, the implications and limitations of this study were discussed.