The research is for meta-analysis on the effect of group play therapy on children with ADHD. For this, research materials were selected from study results in Korea released from 2000 to Sep. 2016. The data were analyzed using academic DB; 2,539 theses proper for the research objective were found from the 1st search word, 623 from the 2nd search word, and 12 from the 3rd criteria. Using CMA program, 26 effect sizes were estimated. The result is as follows: First, as a result of investigating group play therapy programs in the target theses, research on children with ADHD has continued since 2000, and mediating methods also been conducted in various ways. Second, the average effect size of all the group play therapy was 1.479, which indicates that effect size was fairly big. Third, as for effect sizes of group play therapy on children with ADHD according to mediating variables, it was effective for children with ADHD with emotion based group play programs (7.539), a single grade of students (1.685), number of students less than 7 (1.908), number of sessions 11∼15 (1.850), and required time for a session more than 51 minutes (1.861).