The purposes of this research were to measure the effect sizes of sandplay therapy for children and adolescents by conducting meta-analyses, and further provide useful information regarding efficacy of sandplay therapy in addressing child and adolescent problems. A total of 46 treatment outcome studies of sandplay therapy targeting children and/or adolescents (period between 2000-2014) were examined to be analyzed effect sizes in various outcome dimensions. The research also examined the effects of potential moderators on the treatment outcomes. Meta analyses revealed the overall effect size of sandplay therapy being 1.098, suggesting a large effect. In terms of dependent variables, it was confirmed that sandplay therapy is effective in bringing positive changes in child and adolescent cognitive, cognitive/emotional, and behavior/social aspects. With respect to moderator variables, the following variables led to statistically large effect sizes: sandplay therapy addressed in an individual format, sandplay therapy for children with emotional and behavioral problem, sandplay therapy provided twice a week, and sandplay therapy lasting 50 to 60 minutes per session. This research was significant in that it was the first meta-analytic outcome study attempted in Korean in the field of sandplay therapy. Given the results, sandplay therapy seems to be effective therapeutic approach in addressing various child and adolescent problems.