This study involved running a group art therapy program for adults with intellectual disabilities, focusing on self- expression so that we could assess whether changes in art self-expression through group art therapy affect sociality and problem behaviors of intellectually disabled adults. The study targets were a single group of 10 adults with intellectual disabilities aged 19 to 22 years old. and the program was performed for once a week for 60 minutes per session for a total of 21 sessions at the S welfare Center. The pretest, post-test, and follow-up test were performed respectively using the fllowing study tools: art self-expression capability assessment, basic function index of sociality, and adult behavior assessment scale test. The summarized study results were as follows. First, group art therapy had a positive effect on the change in art-self expression of intellectually disabled adults. Second, group art therapy had a positive effect on the improvement in sociality among adults with intellectual disabilities. Third, group art therapy had a positive effect on reducing the problem behavior of adults with intellectual disabilities. The results of the follow-up test were the same as the post-test results.