The purpose of this study was to examine the effects of music therapy based on an improvisation program using imitation and reflection techniques on the stereotyped behavior of autistic children. For this study, three autistic children aged 11 to 13 from S Welfare Center for the Disabled were agreed to participate in the study. This study was designed using the single-subject repeated-measures design method and was an ABA type program which operated 20 sessions in total. In the pre-baseline phase, the children played musical instruments. Then, a non-directed improvisation program which applied imitation and reflection techniques was conducted in the therapeutic musical intervention period. As a result, the stereotyped behavior of each child (child 1: rapping, child 2: rubbing the mouth, and child 3: hand flapping) during the therapeutic musical intervention period was reduced 60%, 29%, and 70% respectively compared to the pre-baseline phase. In the post-baseline phase, the stereotyped behavior of each child increased compared to the therapeutic musical intervention period, although compared to the pre-baseline it was reduced 28%, 19%, and 41% respectively. Therefore, the results of this study suggest that the stereotyped behavior of autistic children can be reduced significantly more by a non-directed improvisation program which applies imitation and reflection techniques than by solely playing instruments.