This study investigated the effects of group art therapy on the peer relationship and the emotional expression of adolescents with poor school adjustment. Students were administered a school adjustment test, the result of which showed that 14 students had problems in adjusting to their school life. The 7 students were designated as an experimental group(7 females) and a control group (7 females). The experimental group received an 8 session art therapy, once a week, each session 60 minutes long. The instruments included an emotions scale and peer relationship scale, all of which were administered before and after the group art therapy program. Data were analyzed using Wilcoxon rank sum test, a non-parametric verification. The findings of this study are as follows. First, all the members in the experimental group showed improvement in the whole domain of emotional expression and the subcategories including self-perception and positive⋅negative ambivalence. This finding suggests that group art therapy improved the self-perception of the participants and reduced their positive⋅negative ambivalence, which contributed to their emotional expression. Second, all the members in the experimental group showed improvement in the whole domain of peer relationship and the subcategories including existence of friends and the trust, duration of the relationship between friends, adjustment between friends, and activities between friends. This finding suggests that group art therapy improved the existence of friends and trust, which lengthened the duration of the relationship between friends and that art therapy improved the adjustment between friends and activities, which made positive effects on the peer relationship.