Objectives : The aim of this study was to investigate the prevalence of metabolic syndrome and the association between lifestyle factors and the risk of metabolic syndrome in Korean adolescents. Methods : The metabolic syndrome was defined with ${geq}$ 3 metabolic abnormalities using the age-modified criteria of the Adult Treatment panel III specified by National Cholesterol Education Program in adolescents aged 12 to 18 years who have participated in the Kroean National Health and Nutrition Examination Survey in 1998(n＝936) and 2008(n＝620). Physical activity and dietary intakes were assessed. Results : The overall prevalence of metabolic syndrome in Korean adolescents declined over 10 years (P < 0.01). Adolescents engaging regular exercise significantly increased over 10 years (P < 0.001). Physically activity was associated with a lower risk of metabolic syndrome (P < 0.001). Dietary intake patterns were not associated with a risk of metabolic syndrome. Conclusions : The prevalence of metabolic syndrome among Korean adolescents declined over 10 years which may be in part due to the increased regular physical activity. The risk of metabolic syndrome is lower in individuals who are physically active.