Abstract: Objective To estimate the prevalence and associated factors of violence among middle school students in Ningbo city.Methods A total of 10 787 students from 70 middle schools were recruited through multi-stage random sampling.All data were collected by self-reported questionnaire regarding demographic information,self-directed violence,physical violence and cyberbully,which was modified from the Youth Risk Behavior Surveillance System in USA.Results In the last 12 months before the survey,20.20% students reported violent behaviors.Specifically,12.88% students had been in a physical fight at least one time,and 68.83% of which happened on school property.About 2.40% and 5.36% students had been bullied on school property and cyberbullied respectively.And 5.42% of all students reported self-directed violence and 30.09% of which needed treatment in hospital.Results of multivariate logistic regression indicated that male(OR=5.51,3.32,1.72),urban(OR=1.23,1.48,1.35),the abnormal marital status among their parents (OR =2.04,1.50 and 1.84) could increase the risk,while higher grade (OR =0.78,0.88),living with their parents (OR=0.81,0.63,0.61) and myopia (OR=0.71) could reduce the risk of physical fighting,selfdirected voilence,and cyberbully.Conclusion Adolescent violence is a common concern.Males,students in lower grade and those with separated parents in middle schools are especially vulnerable to bullying.Prevent and address bullying behavior should be embedded within a comprehensive bullying prevention strategy.