This study was conducted to examine the moderated mediation effect of self-esteem through internet overdependence on the effect of academic stress on depression and anxiety. Surveys were conducted as part of the 13th wave of the Korea Welfare Panel Study. The survey included academic stress, internet overdependence, depression and anxiety, and self-esteem scales. A total of 383 middle school students completed surveys. Data was analyzed using SPSS 21.0 and SPSS PROCESS Macro. There were three major results. First, internet overdependence partially mediation the effect of academic stress on depression and anxiety. Second, self-esteem moderated the relationship between internet overdependence and depression and anxiety. Third, self-esteem also moderated the mediating effect of academic stress on depression and anxiety through internet overdependence. These results indicate that self-esteem is a protective factor against the negative effects of internet overdependence on mental health and of academic stress on depression and anxiety in middle school students. This paper discusses the implications of these results, this study's limitations, and suggestions for future studies.