Objective: The study aim was to explore associations between daily physical activity level, cardiorespiratory fitness and metabolic syndrome among Chinese children. Design: We conducted a school-based, cross-sectional study. Setting: Participants including 112 boys and 121 girls were recruited from three schools in the urban suburbs of Tianjin city, China. Methods: A total of 233 children (12-15 years old) were recruited from the urban suburbs of Tianjin, China. Their daily physical activity level was monitored using accelerometry. Cardiorespiratory fitness was evaluated through a predicted maximal oxygen uptake. The prevalence of metabolic syndrome and its basic components were determined. Correlations between specific components of metabolic syndrome and daily physical activity and maximal oxygen uptake were assessed. Results: In all, 5.4% of the boys and 2.5% of the girls had metabolic syndrome, identified by the modified International Diabetes Federation definition. Moderate physical activity level had a negative correlation with blood pressure, but did not correlate with other components. Predicted maximal oxygen uptake displayed significant correlations with more components of childhood metabolic syndrome than those of physical activity level. Conclusion: Daily physical activity level did not show a significant correlation with the components of metabolic syndrome in 12- to 15-year-old Tianjin city children. However, planned exercise with a goal of improving maximal oxygen uptake should be stressed in school physical education in order to prevent the development of childhood metabolic syndrome.