Introduction: Adolescents who witness bullying often stand by passively rather than supporting their victimized peers with prosocial defending. In this study, we investigated whether compassion, as unique from empathic distress and anger and social costs, related to more prosocial and less aggressive defending and passivity. Method: Australian adolescents (N = 210; M[subscript age] = 14.66, SD = 1.11, age range = 13-17 years; 56% girls) completed surveys that also included embedded film clips portraying peer social bullying. Adolescents reported their compassion, empathy, perceived costs, and intended defending following each clip, and reported their recent experience with bullying and defending. Results: A multivariate path model revealed that adolescents higher in compassion, but also in empathic distress and empathic anger, intended more prosocial defending. Yet, only compassion was associated with less aggressive defending and empathic anger was associated with more aggressive defending. Empathic distress and social costs associated with more passivity, but compassion and empathic anger associated with less passivity. Conclusion: This study provides the first evidence of unique and differential associations of empathic distress, empathic anger, compassion, and perceived social costs with different bystander behavior intentions among adolescents. Importantly, the findings support the distinctive role of compassion in constructive prosocial and lower aggressive defending.