Purpose. The purpose of this study is to investigate effects of group play therapy program on improvement of social skills of children with developmental disabilities. Methods. With 4-year children with developmental disabilities with developmental problems, group play therapy program with 16 sections, 40minutes for each section for 16 weeks was conducted, and by using Korean infant social skills test (K-SSRSP), social skills index (SSQ) between before and after applying group play therapy program on children with developmental disabilities were compared. Results. When group play therapy are applied on children with developmental disabilities, it was found that there was improvement of social skills including problem solving, emotional expression, sense of order and self-confidence. Conclusions. According to the result of this study, if more specific studies regarding group play therapy program are conducted and they can reflect on other integrated programs, then it is expected that there will be greater synergy effects on improving not only children with developmental disabilities but also social skills of them.