This study comprehensively examined the effects of treatment interventions for Internet addiction among adolescents in South Korea through a meta-analysis. We analyzed 70 domestic master's theses and journal articles that reported on controlled studies and involved pre- and post-test analyses in the design. The dates of these publications fall between 2000 and 2015. The total effect size, calculated by random-effect analysis (g), revealed that interventions for the treatment of Internet addiction were effective (ES=1.838). Meta-ANOVAs revealed differences between groups based on a theoretical model, intervention group size, and intervention duration. Integrative therapy produced larger effect sizes (ES=2.794) compared to other treatment models such as cognitive behavioral therapy and reality therapy. Effect sizes for interventions, including nine to 12 people (ES=2.178), were larger than those of interventions including more or fewer participants. Finally, treatment interventions that lasted 8 or more weeks revealed larger effect sizes (ES=2.294) compared to shorter interventions. The study findings suggest directions for the development and effective operation of future Internet addiction interventions among Korean adolescents. Increasing the effectiveness of these interventions requires an integrative theoretical model, an intervention group size of nine to 12 participants, and a long-term intervention.