This study examined the links between seven specific mechanisms of moral disengagement and indirect bullying, direct bullying, and pro-aggressive bystander behavior. In addition, the moderating role of gender on these associations was examined. Participants were 317 Swedish students in Grades 4 to 8 (M_age=12.6, SD = 1.35; 62% girls). Multivariate multiple regression analyses showed that indirect bullying was predicted by gender and victim attribution. Direct bullying was predicted by moral justification, and for girls, by victim attribution. Pro-aggressive bystander behavior was predicted by diffusion of responsibility, victim attribution, gender, and age. That is, boys and younger students were more prone to take the aggressor’s side compared with girls and older students. Furthermore, the relation between pro-aggressive bystander behavior and distortion of consequences appeared stronger in boys than in girls. These results highlight the relative importance of specific moral disengagement mechanisms and may have implications for interventions targeting bullying.