Adolescents’ defending behaviors in school bullying situations is likely determined by individual characteristics, social status variables, and classroom/school contextual factors operating simultaneously in the peer ecology. However, there is little research on defending behavior that utilizes this multilevel approach. This study investigated how students’ willingness to defend victims of bullying was affected by feelings of empathy, perceived popularity, and classroom-level perceived prosocial norms. Participants were 1373 adolescents (40% girls, Mage: 14 yrs) from 54 classrooms in six middle schools in South Korea. These youth reported on their feelings of empathy and how prosocial they perceived their classmates to be. Peer-ratings and peer nominations were used to estimate defending behaviors and which students were perceived as popular. Multilevel analyses showed that participants were more likely to defend victims when they had greater empathy and perceived popularity and when classroom-level prosocial norms were higher. The findings have implications for interventions to reduce school bullying and for studying defending behavior in multiple cultural contexts.