---

Abstract Background and Aim: Reduction of physical activity among adolescents is one of the most important problems of society. The aim of this study was to determine the effects of training programs on promoting the physical activity among school students by using the theory of planned behavior. Materials and Methods: This was a quasi-experimental study in which four junior high schools were randomly selected and then assigned to two interventional groups (n=150) and two control groups (n=150). Next, the students filled out the questionnaires before the intervention and two months after the intervention. The collected data were analyzed using SPSS Software V.13 employing Chi-square, independent and paired t test. Results: There was a statistically significant difference for the mean score of attitude (p=0.003), intention (p=0.000), subjective norms (p=0.013), perceived behavioral control (p=0.001) and increasing physical activity (p=0.000) among interventional groups after implementing the educational program. Conclusion: The overall results indicated that there were significant differences in the structure of theory of planned behavior and the increase of physical activity among students in the intervention group after training. It seems that implementing educational programs for increasing physical activities among students will be useful.