In view of growing adolescent Internet addiction (IA) in the global context, there is a great need to understand the predictors of IA and design related evidence-based intervention and prevention programs. This longitudinal study investigated the relationships between Positive Youth Development (PYD) attributes and IA problems and the mediating role of life satisfaction using a large sample of Chinese high school students (N = 2648). Separated by one academic year, students completed a questionnaire evaluating their adolescent psychosocial adjustment, including validated PYD and IA measures. Multiple regression and structural equation modeling analyses were used. Consistent with the theoretical predictions of PYD models, results revealed a significant negative influence of PYD attributes on IA symptoms concurrently and longitudinally. In particular, general PYD attributes, such as emotional competence, spirituality, and resilience, showed strong and stable protective effects against IA. Life satisfaction also served as a mediator of the influence of all measures of PYD attributes on IA symptoms. The study underlines the importance of PYD attributes in promoting adolescents’ life satisfaction and preventing IA, and thus contributes to the design and implementation of evidence-based intervention and prevention programs.