BACKGROUND Parents play an important role in the development of children's health behaviors, but less is known about the role of parental encouragement for physical activity (PA) on youth PA behavior and body image satisfaction. The purposes of this study were to: (1) longitudinally assess whether adolescent PA at age 15 mediates the effect of perceived parental encouragement for PA at age 15 for predicting adolescent body satisfaction at age 16, while controlling for body mass index (BMI), and (2) examine the extent to which adolescent sex moderates this association. METHODS Participants were 379 boys and girls assessed at 15 and 16 years of age, who completed surveys as part of a larger longitudinal study in their health/physical education classes in a school district in Central Pennsylvania. Participants completed measures of their perception of parental encouragement for PA, PA behavior, body satisfaction, and height and weight to calculate BMI at age 15 and 16 (i.e., 10th and 11th grades). Pearson correlations were used to examine the association among the study variables and hierarchical regression analyses were used to predict body satisfaction at age 16. RESULTS Perceived encouragement for PA from fathers, but not mothers, at age 15, was significantly associated with adolescent PA at age 15 and body satisfaction scores at age 16. Adolescents reporting higher PA behavior and perceived encouragement for PA from fathers at age 15 had higher body satisfaction scores at age 16. Moreover, adolescent PA at age 15 mediated the association between perceived fathers' encouragement for PA at age 15 and adolescent body satisfaction at age 16, when controlling for BMI. Examining the moderating effect of adolescent sex on this association revealed that adolescent PA no longer mediated the association between perceived encouragement for PA from fathers and adolescent body satisfaction, and sex moderated this association. CONCLUSIONS These findings suggest that, regardless of adolescent BMI, fathers may play an instrumental role in adolescents' body image satisfaction by positively influencing PA behavior. However, the influence of perceived encouragement for PA from fathers on adolescent body satisfaction and PA behavior may differ for boys and girls.