Objectives: The term “outsider behavior” refers to the practice of not responding to cyberbullying, while the term “defender behavior” involves reacting to the perpetrator’s actions and seeking assistance from friends to support the victims. This study examined behavior mechanisms in the context of cyberbullying, focusing on the role of maternal anxious rearing behavior and the mediating roles of adolescents’ self-efficacy and moral motivation.Methods: The study participants were 234 adolescents (Mage = 13.92, SD = .96) who witnessed cyberbullying while attending middle schools in South Korea. Adolescents’ perceived maternal anxious rearing behavior, self-efficacy, moral motivation, and cyberbullying outsider and defender behavior were measured using self-reported questionnaires. Data analyses were conducted to examine descriptive statistics using SPSS and a structural equation model using AMOS.Results: The results indicated that while maternal anxious rearing behavior is not directly associated with cyberbullying outsider behavior, it is significantly associated with lower levels of cyberbullying defender behavior. Higher levels of maternal anxious rearing behavior are associated with lower levels of self-efficacy in adolescents, leading to lower moral motivation, which, in turn, is associated with an increase in cyberbullying outsider behavior. In contrast, moral motivation is not significantly associated with cyberbullying defender behavior.Conclusion: Adopting an integrated perspective, our findings underscore pathways to shaping different cyberbullying behavior in adolescents linked with their perceived maternal anxious rearing behavior, self-efficacy, and moral motivation. These findings highlight the crucial role of maternal anxious rearing behavior in practical implications, suggesting the need for effective interventions when adolescents witness cyberbullying.