Objective: To examine the role of social support (SS) and self-efficacy (SE) for physical activity (PA) in rural high school girls (N = 259, 15.5+1.2yrs). Methods: Using structural equation modeling, the relationships among PA, SS for PA from mother, father, and peers, and SE for overcoming barriers, seeking support, and resisting competing activities were tested. Results: The effect of peer SS on PA was partially mediated through overcoming barriers. The effect of support seeking on PA was fully mediated through peer SS to overcoming barriers. Neither parent influenced PA. Conclusions: Peer SS and specific dimensions of SE should be considered in intervention studies.