Objectives: The aim of this study was to investigate the prevalence of metabolically obese, normal-weight (MONW) phenotype and the association between lifestyle factors and the risk of MONW in Korean adolescents. Methods: Normal-weight (BMI, 5th to 85th percentile) subjects with ${geq}1$ metabolic abnormalities were categorized as MONW phenotype. Data from adolescents aged 12 to 18 years who have participated in the Korean National Health and Nutrition Examination Survey in 1998 (n=751) and 2008 (n=455) were analyzed. Physical activity and dietary intakes were assessed. Results: The prevalence of hypertension and hyperglycemia in 2008 decreased compared with that in 1998 (P<0.001) but the prevalence of abdominal obesity, hypertriglyceridemia and low HDL did not changed. The overall prevalence of MONW in Korean adolescents declined over 10 years (P<0.001). Adolescent boys and girls engaging regular exercise significantly increased over 10 years (P<0.01). Physically active adolescents had a lower risk of being MONW in 1998. Dietary intake patterns were not associated with a risk of MONW. Conclusions: The prevalence of MONW among Korean adolescents declined over 10 years which may be due to the decreased prevalence of hypertension and hyperglycemia. The risk of MONW would be lower in individuals who are physically active.