Purpose: Based on self-determination theory, the purpose of this study was to analyze the relationship between social physique anxiety and intention to be physically active, while taking into account the mediating effects of the basic psychological needs and behavioral regulations in exercise. Method: Having obtained parents' prior consent, 390 students in secondary school (218 boys, 172 girls; M[subscript age] = 15.10 years, SD = 1.94 years) completed a self-administered questionnaire during physical education class that assessed the target variables. Preliminary analyses included means, standard deviations, and bivariate correlations among the target variables. Next, a path analysis was performed using the maximum likelihood estimation method with the bootstrapping procedure in the statistical package AMOS 19. Results: Analysis revealed that social physique anxiety negatively predicted intention to be physically active through mediation of the basic psychological needs and the 3 autonomous forms of motivation (i.e., intrinsic motivation, integrated regulation, and identified regulation). Conclusion: The results suggest that social physique anxiety is an internal source of controlling influence that hinders basic psychological need satisfaction and autonomous motivation in exercise, and interventions aimed at reducing social physique anxiety could promote future exercise.