Based on self-determination theory (SDT), the goal of this study was to analyze the relation between satisfaction of basic psychological needs, types of motivation to exercise, and social physique anxiety (SPA). Participants in the study were 398 secondary education students, aged between 12 and 19 years, who completed questionnaires that measured the variables of interest. The results of multiple mediation analysis revealed that satisfaction of the need for competence negatively predicted SPA, both directly and indirectly through the mediation of integrated, identified, and external regulations. Introjected regulation also positively predicted SPA. Gender and body mass index (BMI) affected the relationships analyzed and were also shown to predict SPA. The results of this study further our understanding of the motivational process that explains SPA in adolescents within an exercise context, showing the positive influence of perceived competence and types of self-determined motivation to reduce SPA.