Abstract: Objective To explore the association between screen time and overweight and obesity among children and adolescents in a week,on weekdays and weekends,and to provide a reference for improving overweight and obesity of primary and middle school students.Methods By the method of stratified cluster sampling,16 schools (4 urban middle schools,4 rural middle schools,4 urban primary schools,4 rural primary schools,respectively) located in Fangshan district were selected.Students were required to record their daily physical activity,height and weight for seven days.The association between screen time and their overweight and obesity during the whole week,weekday and weekend were analyzed.Results The prevalence of overweight and obesity among the participants was 32.28%,2.13% of students reported their screen time in weekday was over 3 hours.But in weekend,16.10% of students' screen time achieved more than 3 hours.Compared with students whose screen time was less than 2 hours,those with screen time in the whole week higher than 2 hours or 3 hours were at 1.388 or 1.590 times risk of being overweight and obesity,controlling for the available confounders.In the same way,those with screen time in weekday higher than 2 hours or 3hours were at 1.553 or 1.775 times risk of being overweight and obesity,controlling for the available confounders.But the similar association was not observed in the weekend.Conclusion Screen time more than 2 hours in weekday and the whole week is the risk factor for overweight and obesity among children and adolescents.The students' screen time between weekday and weekend are different which worth more attention.