The aim of the present study was to investigate how basic moral sensitivity in bullying, moral disengagement in bullying and defender self-efficacy were related to different bystander behaviors in bullying. Therefore, we examined pathways that linked students' basic moral sensitivity, moral disengagement, and defender self-efficacy to different bystander behaviors in bullying situations. Three hundred and forty-seven teenagers completed a bullying survey. Findings indicated that compared with boys, girls expressed higher basic moral sensitivity in bullying, lower defender self-efficacy and moral disengagement in bullying. Results from the SEM showed that basic moral sensitivity in bullying was negatively related to pro-bully behavior and positively related to outsider and defender behavior, mediated by moral disengagement in bullying, which in turn was positively related to pro-bully behavior and negatively related to outsider and defender behavior. What differed in the relations between outsider and defender behaviors was the degree of defender self-efficacy. (Contains 2 tables and 2 figures.)