||To overcome the threat of overweight/obesity in adolescents, theory-based inter-ventions promoting physical activity (PA) participation have been widely advanced. Pro-tection motivation theory (PMT) has been moderately effective in the prediction of health-related behavior. Implementation intention (a volitional strategy) interventions have been successful in changing a range of health behaviors. This study examined the impacts of PMT-based motivational intervention and implementation intention-based vo-litional interventions on PMT constructs, PA intention and behavior. The study also com-pared the cognitions of PMT constructs, PA intention and behavior between over-weight/obese adolescents and normal weight adolescents. Finally, the study tested the predictive strength of PMT constructs on PA intention and behavior among adolescents. A total of 330 junior high school students were assigned to either a control group or one of the two experimental conditions: motivational intervention or a motivational plus volitional intervention. Motivational intervention included reading a leaflet about overweight/obesity and the effects of PA on preventing the threat. Volitional intervention involved asking participants to plan when and where they would participate in PA. Partic-ipants' PMT constructs, PA intention and behavior were measured at three time-points over a four-week period. iv MANOVA with repeated measure yielded a nonsignificant main effect for inter-ventions on PMT constructs, PA intention and behavior, whereas a significant main effect for weight category on PMT constructs, intention and behavior was detected. Follow-up tests indicated that overweight/obese adolescents reported significantly higher perceived vulnerability and response cost, and lower self-efficacy, physical activity intention, and behavior than normal weight adolescents did. Hierarchical regression revealed that the entire PMT model accounted for 14% of variance in PA behavior. Specifically, intention, perceived vulnerability, and response cost were significant predictors of PA behavior. Additionally, PMT constructs explained 40% of variance in intention. Self-efficacy and response cost emerged as significant predictors of intention. The findings indicated that compared to the control group the interventions were not effective in promoting adolescents' PA intention and behavior. However, the evi-dence for the utility of PMT in predicting PA intention and behavior among adolescents was provided. Overweight/obese adolescents need to enhance their self-efficacy and re-duce their perceptions of PA costs.