This study was conducted to examine the moderating and mediating effect of ego - resilience, parenting attitude, and peer attachment in the relation between smartphone dependency and aggression. Participants were 1,863 youths using a smartphone among the first middle school students responded in the 7th Korean Children and Youth Panel Survey (KCYPS) conducted by the National Youth Policy Institute in Korea. The data were analyzed by descriptive statistics, a correlation, and a hierarchical regression analysis. First, ego-resilience showed a partial mediating effect on the relationship between smartphone dependency, aggression and significant moderating effects were revealed. Second, parenting behavior showed a partial mediating effect on the relationship between smartphone dependency and aggression, with no moderating effects seen. Third, peer attachment had a partial mediating effect on the relationship between smartphone dependency and aggression, with no moderating effects seen. The research suggested the mental health and growth of students could be improved by applying various nursing and health care programs to improve ego-resilience, parenting behavior and peer attachment as they grow into adulthood.