The literature on the role of participants in bullying lacks empirical studies that attempt to explain the distinction between active defending and passive bystanding. To bridge this research gap, this study adopted structural equation modeling (SEM) to investigate the prospective link between peer status and these two diametrically opposed bystander behaviors in bullying situations, as well as the chain mediating role of social self-efficacy and moral disengagement. Participants were 906 adolescents (392 girls [42.16%], M-age = 15.05 years, SD = 2.01) in 7th to 12th grades from 24 classrooms in four middle and junior high schools in China. After the gender and age were controlled, the results showed that: (1) peer status was directly associated with both bystander behaviors, specifically, positively correlated with active defending and negatively correlated with passive bystanding; (2) in the process whereby peer status was linked to passive bystanding but not active defending, social self-efficacy played a mediating role; (3) adolescents who were less inclined to moral disengagement were more likely to defend victims, while adolescents who were more morally disengaged were more likely to serve as passive bystanders; (4) social self-efficacy and moral disengagement respectively not only played mediating role but also served as chain mediators between peer status and bystander behavior. These results not only suggest that higher status in the peer group may trigger a pro-victim stance in adolescents, but also emphasize the roles of social self-efficacy and moral disengagement in interpreting the association between adolescents' peer status and their bystander behaviors. The development of future effective intervention programs aimed at preventing bullying in schools would benefit from the important insights provided by the findings of this research.