OBJECTIVES: The physical activity of Korean adolescents and its distribution based on social characteristics have not yet been fully assessed. This study intends to reveal the distribution of physical activity by its subgroups and offer possible explanatory variables. METHODS: The 3rd Korea Youth Risk Behavior Web-based Survey was analyzed for this study. The appropriateness of physical activity was defined by Korea's Health Plan 2010 and physical inactivity was assessed independently. Family affluence scale, parents' education levels, subjective economic status, grade, and school location were considered explanatory variables. All statistical analysis was conducted using SAS ver. 9.1. RESULTS: The proportion of participants engaging in vigorous physical activity was high in males (41.6%), at a low grade (38.5%), within the high family affluence scale group (35.5%). The distribution of participants engaging in moderate physical activity showed similar patterns, but the overall proportion was lower (9.8%). Low family affluence and students with lower subjective economic status reported a higher prevalence of physical inactivity. In multiple logistic regression analysis for physical activity, significant factors included family affluence scale (p<0.05). For physical inactivity, family affluence scale, parents education levels, and subjective economic status were included as significant factors (p<0.05). CONCLUSIONS: The results suggest that the physical activity and inactivity of adolescents may be affected by socioeconomic variables, such as family affluence scale. This implies the need to take proper measures to address these socio-economic inequalities.