This study investigated the factors affecting the efficacy of art therapy by art therapists. For this purpose, self-control as an internal characteristic of art therapists, social support as an external characteristic, and transfer of education and training as a mediating variable were set as research questions. Research tools were established based on the previous study review of self-control, social support, and professional self-efficacy. Also, a questionnaire of these research tools was distributed to 250 active art therapists. Statistical analysis was performed to solve the research problem based on the collected response data from 203 therapists among them. The research results of this study method are as follows. First, art therapists’ self-control resulted in a positive effect on the efficacy of art therapy. Second, the social support of art therapists had a positive effect on the efficacy of art therapy, and only the peer support was statistically and significantly effective among them. Third, the mediating effect of education and training transfer could not be investigated. Based on these contents, the significance and limitations of this study were discussed.