Objectives: This study aims to assess the relationships between individual, social and physical environmental correlates and physical activity (PA) and sedentary behavior (SB) in Korean children. Methods: A total of 1,134 elementary school students (512 boys, 5 th and 6 th graders) in Seoul participated in the survey including self-reported moderate and vigorous intensity PA and SB as well as demographic and psychological correlates. These data were matched them with school- and community-level environmental data from the government sources. The relationships of the multilevel correlates with PA and SE were analyzed using gender-specific hierarchical regression analysis. Results: Boys were more active than girls, but there was no gender difference in SB. Students with higher levels of self-efficacy were more likely to participate in moderate and vigorous PA. There were gender-specific associations between social and physical environments correlates and PA. Boys with higher levels of self-esteem and self-efficacy were less likely to involve in SB. Girls in the 6 th grade were more likely to involve in SB. Conclusions: In order to encourage PA and discourage SB in children, school- and community-level environmental support should be considered along with programs to improve self-efficacy and self-esteem.