Existing literature indicates that a weight-management program that includes diet modification, Physical Activity (PA) instructions and behavioral modification in weight reduction increases obese adolescents' participation in PA. However, the effect of such a program on obese Saudi adolescents is unknown. Objective: To examine the effects of a weight-management program in terms of decreasing Body Mass Index (BMI) and improving participation in PA in obese Saudi adolescents, and to establish whether differences exist between genders in response to a weight-management program. PA was measured by Arab Teens Life Style (ATLS) questionnaire for both groups. Results: A wide range of differences in PA and sedentary time are evident between new and weightmanaged patients and two genders. PA performance was significantly higher among the weightmanaged patients compared with new patients. Also, for boys there were no differences between both groups in PA performance. While, girls' PA was significantly higher among the girls in weightmanaged group compared with girls in new patients group. Weight-managed patients spend significantly less time on the computer and/or the Internet per day compared with new patients. After treatment, the mean BMI among the weight-managed patients slightly decreased. Conclusion: The study findings suggest that the weight-management program could be effective in treating Saudi obese adolescents due to its effect in BMI reduction and greater improvement in PA performance. The surprising result from this study, PA differences between the groups were because of the total PA of girls only, meaning that obesity treatment program can lower the percentage of obesity among women and increase their levels of physical activity.