Many cases of violence occur in schools in Yogyakarta. Many of these cases of violence involve students in the same school. Aggressiveness is a form of violence committed by teenagers in schools, disturbing the community. From previous studies on aggressive behavior tendencies, emotion regulation can be used as a mediator variable in aggressive behavior research. Research conducted reveals that emotion regulation helps a person change negative thoughts into positive ones, so the behavior that appears is constructive, not destructive. The purpose of this study was to determine the role of emotion regulation as a mediator between self-esteem and aggressive behavior tendencies in SMPN A students in Yogyakarta. In this study, emotion regulation is considered necessary in mediating the relationship between self-esteem and aggressive behavior tendencies. This study uses a quantitative survey method. The research subjects were students in grades 8 and 9, totaling 155 students of SMPN A in Yogyakarta and collecting data using a psychological scale measuring instrument. The scales used include the Aggressiveness scale, Self-Esteem Scale, and Emotion Regulation scale. Analysis of the data used is mediation analysis regression. This study found that the role of self-esteem on the tendency of aggressive behavior by controlling emotional regulation was p> 0.05 (p=0.706). The research conducted shows that Emotion Regulation as a Mediator of the Role of Self-Esteem on the Tendency of Aggressive Behavior. Emotion regulation has a fully mediating role.