A substantial body of research has demonstrated that adolescent Internet addiction (IA) brings a series of physical and psychological health issues. Among all factors influencing adolescent IA, parenting styles have been noted to be important predictors of adolescent IA. As such, authoritative parenting is negatively linked to adolescent IA, while authoritarian and permissive parenting are both positively associated with adolescent IA. Ego-resiliency, a personality characteristic reflecting the ability to adapt oneself to stress in a variety of contexts, has been linked with a wide range of factors including both parenting styles and adolescent IA. However, most research to date has only focused on the direct link between parenting styles and adolescent IA, little is known about the specific mechanisms underling parenting styles and IA. Does there exist a mediator or moderator in the relationship between parenting styles and adolescent IA? Determining the mediators and moderators would be important to provide guidelines to prevention and intervention of adolescent IA. Thus, the present study sought to examine the relationship between parenting styles and adolescent IA as well as the potential mediating and moderating roles of ego-resiliency in such a relationship. This study used a stratified cluster sampling to select 2,758 seventh to ninth graders (mean age = 13.35 years, SD = 1.06 ). We recruited participants from ten middle schools in four different cities of Guangdong province. Participants anonymously completed the modified Parenting Styles and Dimensions Questionnaire, Ego-Resiliency Scale, Adolescent Internet Addiction Scale and demographic information questionnaire. We used SPSS 22.0 software and Mplus 7.4 to conduct all statistical analyses. First, we obtained descriptive statistics for our variables of interest and covariates. Next bi-variate associations among all variables were calculated to examine the relationships among variables. Path analyses were then used to examine the mediating and moderating role of ego-resiliency. The major findings of the present study were: (1) Authoritative parenting was negatively associated with IA but positively associated with ego-resiliency, whereas authoritarian and permissive parenting were both positively associated with IA but negatively associated with ego-resiliency, ego-resiliency was negatively associated with IA. (2) Mediation analyses indicated that ego-resiliency mediated the relationships between authoritative/authoritarian parenting and IA. Interestingly, despite the fact that authoritarian parenting positively predicted IA, we also found that authoritarian parenting could positively predict ego-resiliency which in turn negatively predicted IA. (3) Moderation analyses showed that the relationship between authoritarian parenting and adolescent IA was moderated by ego-resiliency. Specifically, the adverse impact of authoritarian parenting was more potent for those who had higher rather than lower levels of ego-resiliency. Findings of the present study provide the first evidence of how and when parenting styles impact adolescent IA through ego-resiliency. Based on these findings, we proposed “the theory of dual effects of ego-resiliency” to explain the fact that ego-resiliency plays both the mediating and moderating roles in the association of parenting styles with IA. The theory posits that the dual nature of ego-resiliency is the reason for its double roles in the association of parenting styles with adolescent IA.