Introduction: Although much research has shown strong relationship between empathy and defender role, less is known about how student-teacher relationship mediated those variables. Our main hypothesis was to reveal whether the student-teacher relationship could be mediating the effect of affective and cognitive empathy on the defender role in bullying at school. Method: A total of 311 participants were selected from 2 secondary schools in south Jakarta. Students refer to grade 7-8 with ranged in age from 13 to 15 years (M[subscript age]= 13.64; SD = 0.713). There were four instruments used: The Basic Empathy Scale to measure affective and cognitive empathy, Behaviors During Aggressive Episodes and Student Bystander Behavior Scale to measure defender role, and Student Perception of Affective Relationship with Teacher Scale. Results: The results revealed both affective and cognitive empathy were found having a positive effect on defender role in bullying situation among junior high school students. However, cognitive empathy was found positively stronger on defender role rather than affective empathy. Furthermore, student-teacher relationship only partially mediated the effect both affective and cognitive empathy on defender role. Discussion and Conclusion: These findings emphasized the urgency of comprehensive program to create defender by enhancing empathy and positive student-teacher relationship to inhibit bullying behavior at schools.