Objective To evaluate the impact of family-school combined sex education among middle school students.Methods This is a school-based intervention study. Four junior middle schools and two senior middle schools in Xuhui District, Shanghai, were selected as study sites involving parents, two junior middle schools and one senior middle school as the intervention group and others as control group. The intervention group was provided with both school and family education which contained giving lectures, distributing leaflets, organizing group discussions and parent-adolescent communicating activities to parents. Data were collected through anonymous and self-administered questionnaires before and after one-year intervention to evaluate the effect of the intervention.Results The average score of parents in the intervention group was higher than that in the control group after intervention. Particularly, the mean score of AIDS knowledge in the intervention group was increased by 10.5, which was more than that of control group (5.3). The intervention increased the patents'intention to family sex education. The percentage of parents in the intervention group approving "sex education should be provided by parents" had increased, much higher than that in the control group. Intervention also promoted parent-adolescent communication about sex.The percentage of parents reporting "they actively talked with their children about sex or their teens asked them questions related to sex" had increased, much higher than that in the control group.Conclusion Family-school combined sex education significantly increased sexual knowledge and sex education intention of parents, promoted the parent-adolescent communication about sex as well.