Moral disengagement processes are cognitive self-justification processes of transgressive actions that have been hypothesized to be learned and socialized within social contexts. The current study aimed at investigating socialization of moral disengagement by friends in two developmentally different age groups, namely late childhood (age: 9-10 years; n = 133, 42.9% girls) and early adolescence (age: 11-14 years; n = 236, 40.6% girls) over a 1-year period. Specifically, the current study examined whether similarity in moral disengagement between friends was the result of friends' influence or friend selection. Moreover, gender (42% girls), individual bullying behavior, and perceived popularity status were examined as potential moderators of socialization for moral disengagement within friendship networks. Self-report measures were used to assess moral disengagement, sociometric questions and a peer-nomination scale for friendship networks and bullying behavior, respectively. Longitudinal social network analysis (RSiena) was used to study change of moral disengagement in friendship networks during a 1-year interval. In early adolescence, friends were more likely to be similar to each other over time and this was explained only by influence processes and not by selection processes. Gender, bullying, and perceived popularity did not moderate the friends' influence on moral disengagement over time. Results indicate that self-justification processes change over time already in late childhood, but only in early adolescence this change is likely to be dependent upon peers' moral disengagement.