Objective · To investigate the prevalence of passive smoking among pregnant women in Shanghai and to analyze its influencing factors and to provide the basis and suggestion for making related intervention measures to reduce the harm of secondhand smoke on the health of pregnant women. Methods ·From July to October 2014, pregnant women and their spouses were recruited for a questionnaire investigation at the antenatal care clinics of 3 maternity hospitals and 3 community hospitals in Shanghai. The questionnaire included demographic information, family basic situation and cognitive status of passive smoking. Results · The passive smoking rate before pregnancy in the 2 831 pregnant women, who were involved in the investigation, was 17.1%. The passive rate during pregnancy was 7.8%. The difference between these two rates was statistically significant (P<0.05). 71.0% of the pregnant women have passive smoking for 15~59 min each day. Relative to home and work place, the passive smoking rate of pregnant women in public place was the highest (P<0.05). The passive smoking rate of pregnant women was significantly associated with the educational level of smoking spouses and the attitude of pregnant women when they faced the smokers. Conclusion · The passive smoking rate of pregnant women is influenced by the educational level of their spouses and the pregnant women’s feedback to the smokers face to face. Public places are the most important exposure places to secondhand smoke for pregnant women. In order to reduce the harm from passive smoking to pregnant women and their fetuses, the related measures of smoking control at home education and smoking ban in public place should be made.