Objectives: This study was conducted to explore the barriers to physical activity in a representative sample of Iranian children and adolescents.Methods: The studywas conducted in 2007 in urban and rural areas of Isfahan district in Iran. In the qualitative part,we used the grounded theory approach, including semi-structured focus group discussionsand in-depth interviews. The quantitative part comprised 600 randomly selected students.Results: The qualitative study included 34 school students (16 girls), 20 parents (11 mothers) and 11 school staff. All students disclosed that studying was a priority.They pointed to lack of safe and easy-access place for physical activity and unsupportive family as the main barriers. Lack of self-confidence and low self-worth were the two other concepts developed in this context.Parents pointed to lack of safe and easy-access place for activity followed by the priority of studying. The concepts derived from interviews with school staff included unhealthy modeling of parents, priority of studying, and inadequate public know-ledge about how to integrate physical activity in routine daily life.The quantitative survey comprised 600 students including 286 (47.8%) girls. Parents’ education level had inverse association with children’s physical activity level. Significant inverse associations of self-efficacy and physical activity levels were documented.Conclusions: Increasing the public knowledge about adopting physical activity habits in routinedaily life, informing the families and students about the benefits of physical activity to improvelearning, as well as providing safe places such as using the school facilities in non-school hoursshould be considered in planning effective preventive strategies and interventions