Objectives: This study investigated obesity adolescents in Korean. Methods: This study was a cross-sectional, secondary analysis using the 2021 Korea Youth Risk Behavior Survey data. Among 54,848 adolescents in the raw data, 53,445 adolescents were selected as study participants. Results: It was found that sex, school achievement, fast food intake frequency, sitting time other than weekend learning, and weekend smartphone usage time were important individual factors influencing obesity in adolescents. It was found that school type was community and societal factors influencing obesity in adolescents. Conclusions: It is necessary to develop a obesity education program that considers eating habits, sedentary behavior, smartphone use, and school type of adolescents.