BackgroundTo analyze the associations among autonomous motivation, self-efficacy, satisfaction of basic psychological needs, social support and perceived environment with physical activity practice of adolescents aged between 12 and 15 years; and to test autonomous motivations and self-efficacy as potential mediators of the associations between these environmental factors and physical activity practice.MethodsWe evaluated 553 adolescents, that participated in the ActTeens Program. Physical activity was assessed using the Physical Activity Questionnaire for Adolescents. Autonomous motivation, self-efficacy, satisfaction of basic psychological needs, parents’ social support and perceived environment were assessed using specifics questionnaires. Linear regression models were used to test the associations.ResultsParents’ support (β = 0.32), satisfaction of basic psychological needs of colleagues (β = 0.21) and teachers (β = 0.12), and perceived environment (β = 0.10) had significant associations with physical activity (p < 0.05). The direct effect value was reduced when autonomous motivation was added as a mediator of the association between parents’ support and physical activity (β = 0.24), with a 25% mediated effect. Autonomous motivation was mediator of the relationship between basic psychological needs of colleagues (β = 0.13; EM = 38%), teachers (β = 0.02; EM = 83%), and perceived environment (β = 0.03; EM = 70%) with physical activity.ConclusionSelf-efficacy was not associated with physical activity and autonomous motivation was an important mediator of adolescents’ physical activity.