The importance of physical activity as a health promoting behavior has been well documented. We examined the relationship of social support, self-efficacy, and commitment to a plan of physical activity on physical activity behaviors in a sample of low income college students. Those with higher levels of social support, self-efficacy, and commitment to a plan of physical activity reported more physical activity behaviors. Commitment to a plan of physical activity mediated the relationships of social support and physical activity behavior, and of self-efficacy and physical activity behavior. The results support the importance of exploring the psychosocial correlates of physical activity in explaining the decision process that underlies physical activity behavior.