Purpose: This study investigated the effects of lifestyle factors in metabolic syndrome among adolescents. The metabolic syndrome has been reported as a cause of various chronic diseases, including cardiovascular disease and diabetes in adolescents. Method: This study is a cross-sectional study on 1,931 adolescents (1,011 boys and 920 girls) aged 12-19 years from the Korean Health and Nutrition Examination Survey 2010-2012. Data were analyzed by descriptive statistics, t-test, $x^2$-test, and logistic regression in consideration of strata, cluster, and weight as national data. Result: The prevalence of metabolic syndrome in adolescents aged 12-19 years was 4.3% (Boys, 5.4%; Girls, 3.1%). Among lifestyle factors, BMI had significants influences on the metabolic syndrome risk, but other variables did not. Conclusion: The results of this study indicate that further research is necessary on the effect of lifestyle factors in metabolic syndrome and that school health nurses should focus on implementation of effective programs for promotion of activity and healthy foods for prevention and intervention of metabolic syndrome.