Purpose. To evaluate children’s psychosocial and environmental factors associated with sedentary behavior (SB). Method. The study involved a total of 420 children (mean 9.2 years; 52.9% girls) from the community of Madrid, Spain. SB and physical activity (PA) were objectively measured using accelerometers. TV viewing and potential correlates were assessed by questionnaire. Mixed-model regression analysis, adjusted for clustering within school locations, evaluated the relation of each independent variable with SBs. Results. Girls showed higher levels of SB than boys, whereas boys reported more TV viewing (p<.001 in all cases). Regression analysis showed that MVPA levels were negatively related to objective SB measurement in both boys and girls (p<.001). Parent and friend support to PA were negatively associated with SB on weekdays in boys and girls, respectively (p<.05). In the boys’ group, parental professional level was a positive predictor of SB on weekend days (p=.011). Boys with more positive neighborhood perceptions spent less time watching TV (p<.001), whereas mother’s leisure-time PA level was a negative correlate of TV viewing in girls’ group (p<.01). Conclusion. Different psychosocial and environmental correlates of SB were identified. Present findings are promising targets for interventions to improve children’s health.