Research interest has increasingly focused on the psychosocial factors related to online game addiction. This study examines the relationship of various psychosocial variables to online game addiction, and the mediation effect of avatar identification on the relationship. Questionnaires assessing self-esteem, depression, social skills, game addiction, and avatar identification were completed by 163 third-year middle school students. Correlation and structural equation modeling analyses were conducted. Results indicated (a) that self-esteem and social skills had significant negative correlations with game addiction, while depression had a significant positive correlation with game addiction, (b) that depression had an indirect effect on game addiction via avatar identification, and (c) that social skills had both indirect (via avatar identification) and direct effects on game addiction. Implications and future directions are discussed.