The purpose of this study was to examine the effect of art therapy using three-dimensional formative materials on the problematic behaviors of an ADHD child. The subject of this study was an 11-year-old boy in the fourth grade of C Elementary school located in S City. From June to December 2019, there were a total of 18 sessions for 60 minutes once a week, excluding pre and post-tests. Korea-Child Behavior Checklist(K-CBCL) applied before and after art therapy to compare and analyze the changes. In addition, using the three-dimensional formative materials, the changes in an ADHD child by treatment stage were summarized and analyzed. This study adopted a mixed study method designed by Creswell(2005). Its results were as follows. First, the comparison of pre and post-tests for the Korea-Child Behavior Checklist(K-CBCL) in problematic behavior showed the reduction of aggression, rule-breaking behavior, attention difficulties, and thought problems, implying that art therapy using three-dimensional formative materials had a positive effect on reducing the problematic behaviors of an ADHD child. Second, based on artwork, treatments, and verbatim record, the analysis of the stage changes of problematic behaviors, showed that art therapy using three-dimensional formative materials had a positive effect on reducing the problematic behaviors of an ADHD child. Based on these results, the implication and limitations of this study were discussed.