This study investigated the mediating effect of the therapist's self-efficacy and the moderated mediating effect of the supervisory relationship between art therapist's socially prescribed perfectionism and performance anxiety. For this purpose, the study surveyed targeting 184 art therapists working at counseling organizations across the country using the Socially prescribed Perfectionism Scale, Self-Efficacy Scale, Performance Anxiety Scale, and Supervisory Relationship Scale. The collected data were analyzed using SPSS 25.0 and PROCESS Macro 3.3.1 programs. The results were as follows. First, art therapists' socially prescribed perfectionism showed a positive correlation with performance anxiety and a negative correlation with self-efficacy and supervisory relationship. Second, the mediating effect of self-efficacy confirmed its meaningfullness in the relationship between socially prescribed perfectionism and performance anxiety. Third, the moderating effect of the supervisory relationship in the relationship between socially prescribed perfectionism and self-efficacy revealed its significance. Fourth, the moderated mediating effect of the supervisory relationship was significant in the relationship between socially prescribed perfectionism, self-efficacy, and performance anxiety. Based on these research results, the significance and limitations of this study were discussed.