This study investigated the role of over-adaptation and evaluation of emotion as stress vulnerability factors among Japanese junior high school students. Based upon the diathesis-stress model, 720 students (348 boys and 372 girls) completed questionnaires about stress responses, over-adaptation, and evaluation of emotion. Two weeks later, they completed the questionnaire about stress responses along a questionnaire about school stressors. Hierarchical multiple regression analysis indicated that boys with high over-adaptation tendencies reported a greater stress responses following the occurrence of negative school stressors than non-over-adaptive students. In addition, evaluation of emotion was found to interact with stressors to predict stress responses in boys. These results were not found in girls.