Objective To examine the changes in tobacco related knowledge,smoking habit and the amount if environmental tobacco smoke (ETS) among urban population before and after the enforcement of the Smoke Control Ordinance in Public Places of Hangzhou in March 2010.Methods Two independent cross-sectional surveys were conducted on random samples from adults aged 18-64 years in three districts of Hangzhou city between two petiods:October 2008 to August 2009 and June 2011 to February 2012.Results A total of 2016 adults at the initial stage and 2016adults during the follow-up program completed the survey.Nine out of the ten indices related to the knowledge on tobacco presented an improvement during the follow-up process.All the participants (22.4％ vs.17.7％,P＜0.001) and men (44.2％ vs.37.3％,P=0.004) showed statistically significant declines in the prevalence of smoking,when compared with women (1.7％ vs.1.2％,P=0.379).The proportions of individuals who had noticed anyone smoking in the previous 30 days demonstrated statistically significant declines in nine types of places:school (5.6％ vs.2.7％,P＜0.001),health centre (11.4％ vs.3.7％, P＜0.001),public transportation (19.2％ vs.12.2％,P＜0.001),government building (11.3％ vs.5.6％,P＜ 0.001),restaurant (67.0％ vs.61.3％,P=0.002),workplace (49.7％ vs.38.3％,P＜0.001),private office building (23.6％ vs.19.9％,P=0.023),home (41.0％ vs.35.5％,P=0.003),friend's home (33.9％ vs.29.5％,P=0.017).Conclusion Positive changes were noticed among urban population with respect to tobacco related knowledge,prevalence of smoking,and the environmental tobacco smoke (ETS) after the enforcement of the Smoke Control Ordinance in Public Places of Hangzhou.