Although cyberbullying, a new type of aggressive behavior via electronic means, has been found to be strongly linked with individuals’ personality characteristics, few studies to date have investigated its relationship with narcissism, especially overt and covert narcissism. The current study tested the associations between overt and covert narcissism on one hand and cyberbullying perpetration and victimization on the other. To explain these differences further, self-esteem was tested as a mediator through which the two types of narcissism may exert their influences on cyberbullying. An anonymous questionnaire was completed by 814 Chinese adolescents aged 11 to 18. Results of multiple regression analyses indicated that after controlling for gender and student status (middle or high school students), covert narcissism positively predicted both cyberbullying perpetration and victimization, whereas overt narcissism had no association with either perpetration or victimization. Furthermore, when gender and student status were controlled, self-esteem mediated the relationships between overt/covert narcissism and cyberbullying perpetration and victimization, highlighting the possibility that self-esteem is an explanatory mechanism for the associations between the two types of narcissism and cyberbullying. These findings suggest that interventions aimed at reducing engagement in cyberbullying may be more urgent and important for individuals with high levels of covert narcissism. Boosting self-esteem needs to be particularly highlighted in developing anti-bullying measures and policies.