Objective To investigate the status of passive smoking in middle school students in Shanghai, and explore its relationship with environmental factors. Methods Stratified cluster random sampling method was adopted, and 13 723 students were selected from 29 senior high schools, junior middle schools and vocational schools in Shanghai. On-the-spot questionnaire survey was conducted with selfdesigned questionnaire, which included conditions of smoking and smoking-quitting, knowledge and attitude, passive smoking exposure, media propaganda on smoking and school education on tobacco control, and the survey findings were statistically analysed. Results A total of 13 208 questionnaires were recovered. The prevalences of attempted smoking and current smoking in investigated students were 11.1% and 2.5% respectively, and the prevalences of males were significantly higher than those of females (14.7% vs 7.4%, P<0.001；3.7% vs 1.3%, P<0.001). The prevalence of passive smoking in all the investigated students was 67.0%, the prevalence of females was significantly higher than that of males （68.6% vs 65.4%, P<0.001), and the prevalences of vocational school students and junior middle school students were significantly higher than that of senior high school students (75.6% vs 63.2%, P<0.001; 67.0% vs 63.2%, P<0.001). Among the passive smokers, 34.5% suffered from passive smoking every day. Multivariate Logistic regression analysis demonstrated that females, junior middle school students and vocational school students, students whose parents and friends smoked, students who had less tobacco control education in schools and less contact of anti-smoking media messages, and those who frequently saw actor smoking on media were more likely to suffer from passive smoking. Conclusion The condition of passive smoking is severe in middle school students of Shanghai, and effective measures should be taken to reduce the harm of passive smoking to students with the cooperation of society, school and family.