This study utilizes meta-analysis to investigate the totality of effects of group music therapy on preschool children. For this purpose, a total of 34 effect sizes were derived from 25 dissertations and journal articles published in Korea up until April 2019. The results from the meta-analysis of the data are as follows. The overall effect size of music therapy on preschool children was 1.365 which is a sizable effect. Music play showed the biggest efficacy in the independent variables (song, music listening, movement, music play and combined music therapy). Dependent variables were classified into sociability, emotion, behavior, self-understanding, intelligence, creativity, and stress. Following this classification, the effect size was the largest in the area of self-understanding followed by stress, emotion, intelligence, sociability, creativity, and behavior. Finally, the control variable had a greater effect size when treatment time exceeded 30 minutes.