Abstract: Objective To investigate the relevant influencing factors of the smoking behavior and its influences on future smoking intention of adolescents in Shanghai,and to provide a reference for intervention measures to control their smoking behavior.Methods Stratified random cluster sampling method was used to extract 26 508 students from 68 middle schools in five districts of Shanghai.An anonymous questionnaire survey was conducted.Results The rate of ever smoking was 11.6% in middle school students in Shanghai.The smoking intention in the next 1 year and the next 5 years was 8.0% and 14.1%,respectively.The rates of boys(15.7%,10.9%,19.3%) were higher than those of girls(7.3%,5.0%,8.6%),and the rates of vocational school students (29.2%,21.3%,31.6%) were higher than those in senior and junior middle school(12.5%,9.3%,16.1%).Multivariate logistic regression analysis showed that parental smoking,peer smoking,lack of smoking education in schools,and high exposure to media smoking messages increased the risk of students' attempts to smoke and future smoking intentions(P<0.01).Conclusion Adolescent smoking behavior and future smoking intentions are closely related to family,peer,school and social environment.It is necessary for all parties to work together to take comprehensive and supportive measures to reduce students' smoking behavior.