Using self-determination theory [Deci, E. L., & Ryan, R. M. (1985). Intrinsic motivation and self-determination in human behavior. New York, NY: Plenum Press; Ryan, R. M., & Deci, E. L. (2002). An overview of self-determination theory: an organismic-dialectical perspective. In E. L. Deci, & R. M. Ryan, (Eds.), Handbook of self-determination research (pp. 3–33). Rochester, NY: University of Rochester Press.] as a framework, this study examined the relationships between social physique anxiety (SPA) and physical activity-related psychological needs, motivation, and reported behavior.Three hundred and eighty one males and females (M age =18.69, SD=1.15) completed a self-administered questionnaire package.Results revealed a good measurement model for the total sample (χ 2 =592.52; df=238; RMSEA=.063; CFI=.94; SRMR=.05) and multi-group invariance indicated that the male and female measurement models were comparable. The structural model was adequate for the total sample (χ 2 =638.69; df=243; RMSEA=.065; CFI=.94; SRMR=.06) and accounted for 36% of the variance in reported physical activity behavior. In addition, the structural model was partially gender invariant.Findings supported the proposed motivational sequence in which SPA directly influenced need satisfaction, and indirectly influenced physical activity motivation and behavior. From a practical perspective, interventions aimed at decreasing SPA may be helpful in promoting physical activity motivation and behavior.