This research was conducted to study the effect of group therapy using a cognitive behavioral approach to improve social adjustment of sojourner students at Universitas Indonesia. Social self-efficacy is known as a trait that can affect social adjustment. Some student's problems with social interaction had a negative impact and became a severe psychological problem. Therefore, psychological intervention was required to solve the social adjustment problem by increasing social self-efficacy of sojourner students at Universitas Indonesia. This research used a quasi-experimental design as its method with one group pre-post-test design, by providing group therapy for five participants. The goal of the group therapy was to improve social self-efficacy for sojourner students, which can also be seen in behavior and cognitive aspects. The results of this study measured quantitatively using perceived social self-efficacy (PSSE, Smith and Betz 2003) shows an increase of social self-efficacy in all of the participants. Through qualitative data, the results indicate that cognitive and behavioral aspects changed in all of the participants. The updated cognitive aspects show a changed belief about their own self-efficacy; participants were able to successfully dispute their negative thoughts so that they would have more rational responses. Behavioral aspects show that their behavior in social interactions changed, especially with regard to the initiative of making social contact and joining groups. This research also indicates that using group therapy has advantages for all participants due to the therapeutic effect of learning from other group member's experiences.