This study developed and validated a scale for assessing the competency of art therapists. First, we conducted an exploratory factor analysis of 30 items derived in the design process of art therapist competency model(Kim, 2020) for 112 art therapists, and the optimal questions for each factor. As a result, 21 questions of three factors, including common ability(16 questions), value statement ability(2 questions), and psychological knowledge(3 questions) were derived. Then, we collected additional 221 data from art therapists and conducted confirmatory and validity analyses. The sub-factors and items from the research results were appropriately valid. Also, the competency of art therapists was evaluated through correlation analysis with the client's self-efficacy scale, client's job stress questionnaire, social desirability scale, and personal competence scale. The scale was based on reliability and validity. It was an effective tool. Based on these research results, the significance and limitations of this study were discussed.