The research is about how a free choice activity which is mediated by a teacher according to a monthly theme under integrated education system affects development delayed child’s social behavioral development. The subject of this study were three development retarded children (3,4,5 years old) who attended an integrated ciass of B day care center in J eollanamdo. Applying Mutiple baseline design across subjects, I conducted an activity intermediation by a teacher 15 times according to the free choice activity intermediation program and observed every intermediation process. Then, I recorded any changes in children’s behaviors both in written and by a video camera. As a result, it turned out to be true that the free choice activity intermediation program helps development retarded child to improve his/her social behavior in posltlve ways.