Abstract: Objective To investigate the association between mothers' attendances to pregnancy school and conduct problems in 3-year-old preschool children as well as its potential pathway.Methods A total of 40 237 3-year-old children on their first entrance into kindergartens in the Longhua District,Shenzhen,China during 2014-2016 were selected as the research subjects.We used a general questionnaire to investigate information regarding the demographic characteristics and mother's attendances to pregnancy school,and the Conners' Parent Rating Scale to evaluate children's conduct problems.Cox regression was undertaken to investigate the association between mothers' attending pregnancy school and the offsprings' conduct problems.The stepwise mediation analysis put forward by Baron and Kenny was used to evaluate the mediating effect of passive smoking,breastfeeding and children's outdoor activities in the above association.Results A total of 1 403(3.4%) children scored high above the cut-off value in behavioral problems.After controlling for potential confounders including child gender,parent's education,family income,parent's marital status,etc.matemal pregnancy school absents were associated with higher risks of conduct related problems in their preschool children(PRR =1.23,95% CI =1.11-1.37).Results from further analysis showed that passive smoking during pregnancy,breast feeding,and outdoor activities during 0-3 year of child age mediated 36.8%,3.0% and 5.4% of the aforementioned association,respectively.Conclusion Mothers' prenatal attendances to the pregnancy school can reduce the risk of conduct related problems in 3-year-old children,mainly by reducing the passive smoking during pregnancy,increasing breastfeeding,and increasing children's outdoor activities.