This study investigated how social media use among South Korean adolescents influences life satisfaction, using two-wave panel survey data. Specifically, this study examined the mediating mechanism by which adolescents' social media use is associated with their life satisfaction through social support and social capital. The results demonstrated that social support and social capital mediate the relationship between social media use and life satisfaction. Social media use is positively related to social support, and social support has a positive relationship with a higher level of social capital which, in turn, is related to a higher level of life satisfaction. This study improves our understanding of the relationship between social media use and adolescents' life satisfaction and presents significant implications for those attempting to help such individuals promote their life satisfaction and mental health.