Background: This was a cross-sectional survey to investigate the relationship of age, parent education, sleep duration, physical activity, and dietary habits with overweight or obesity in school-age children in Shanghai. Methods: The survey gathered information from 13,001 children in grades 1 through 5 (age 6 to 10 years) among 26 elementary schools in 7 districts. Activity level was evaluated using the International Children's Leisure Activities Study Survey Questionnaire (CLASS-C). The definitions of normal, overweight, and obese were adjusted for each age. Results: Logistic regression analysis indicated that age, being male, having =10 hours of sleep on non-school days, eating =1 vegetable/day, or drinking =1 sugar-sweetened drink/day increased the risk for a child being overweight or obese compared with having >10 hours of sleep or =3 vegetables or =3 sugar-sweetened drinks/month (p = 0.008). Having >2 hours of outdoor activities on non-school days reduced the risk of being overweight or obese compared with =2 hours of outdoor activities on non-school days (p < 0.001). Conclusions: We found that age, sex, sleep, and some dietary habits impacted weight, and suggests that specific cultural and economic factors may impact risk of a child being overweight or obese.