Internet addiction among adolescents has become a major social problem. Thus, more effective Internet addiction treatment programs through sports are required. This study tried to identify the relationship among sports participation, self-control, and Internet addiction among Korean adolescents. In total, 345 students (aged 15–18 years) from two middle schools and two high schools in South Korea were analyzed using Confirmatory Factor Analysis (CFA) and Structural Equation Modeling (SEM). SEM indicated a significant effect of sports participation on Internet addiction mediated by self-control. The results suggest the effectiveness of and need for sport and physical activity in Internet addiction treatment programs and for other addictions as well. Moreover, sports participation has a wider variety of psychological and physical benefits unlike intervention strategies or pharmacological treatments. Thus, the adoption of sports needs to be broadened from physical development to treating diverse psychological problems among adolescents.