The purpose of this study is to explore the impact on peer-related social interaction of children with developmental disabilities by developing and applying an improvisation program. To this end, an improvisation program was developed based on music curriculum, improvisation techniques, and social interaction teaching methods and applied to three children with developmental disabilities in A Elementary School. The improvisation program was conducted over 20 classes, and the social interaction behavior shown during improvisation was analyzed. In order to confirm the effectiveness of the improvisation program, a reversal design was applied, and visual analysis and effect size analysis were conducted. As a result, the improvisation program increased the behavior of children with developmental disabilities such as smile and laugh, looking at friends, trying conversation. And it was confirmed that the improvisation program was an effective intervention to improve peer-related social interaction of children with developmental disabilities.