The purpose of this study is to examine whether a new construct "Assumed-Competence based on undervaluing others (AC)" could be a determinant of anger and sadness for contemporary Japanese adolescents. A set of questionnaires was administered to 584 high school students, who rated ACS-2 (Assumed-Competence Scale, second version), Rosenberg's self-esteem scale, in relation to their perceived emotional reactions toward certain negative personal and social events, and other scales. The results indicated that the students who got angry at personal events were likely to have high AC. However, those who felt neither anger nor sadness in relation to such social events were likely to have high AC. The role of AC in emotional reactions and suggestions for future research was also discussed. (Contains 4 endnotes.)