The current study investigated the effect of an obesity intervention incorporating physical activity and behavior-based motivational enhancement intervention on BMI, physical activity levels, and psychological variables toward physical activity in male obese adolescents. Single group study without having a control group was carried out in Korea. Sixty-eight obese male adolescents who had BMI greater than 25 kg/m² participated in the 16-week obesity intervention. During this period, the study participants’ BMI, physical activity levels, self-efficacy, and perceived benefits and barriers were measured at the three time point (baseline, after week 8, and after week 16). Results indicated that obese adolescents’ BMI significantly decreased (F = 3.51, p = .03) and physical activity (F = 4.01, p = .02) significantly increased over the 16-week obesity intervention. In addition, Exercise self-efficacy (F = 5.02) and perceived benefits toward physical activity (F = 5.34) significantly increased but perceived barriers of physical activity (F = 5.10) gradually decreased over the intervention. This study suggests that an obesity intervention combining physical activity and behavior-based motivational enhancement intervention significantly contributed to decreased BMI, increased physical activity, and positively changed psychological variables related to physical activity. This first application has resulted in preliminary support for this intervention modality within non-western obese adolescents.