Abstract: Objective To assess the prevalence of smoking behavior and its association with smoking-related knowledge and attitudes and to explore the impacts of family socio-economic status and other main factors on smoking behavior among medical college students in Changsha city.Methods Totally 2 892 medical college students in two comprehensive universities were investigated with a self-designed questionnaire about socio-demographic information,smoking behaviors and related factors.Results For 2 814 students with eligible information,the prevalence rate of lifetime smoking,current smoking and daily smoking was 30.6%(53.3% for male,18.3% for female),3.8%(10.3% for male,0.3% for female),and 0.6%(1.5% for male,0.1% for female),respectively,and 65.5% of the medical college smokers tried smoking when they were in primary schools.The students from rural areas had a higher lifetime smoking rate but lower daily smoking rate than the urban students(32.8% vs 28.1%,0.3% vs 0.9%,respectively).Non-smokers had a higher score for smoking-related knowledge and were more likely to refuse smoking than smokers(P<0.01).A negative correlation was observed between family socio-economic status and the prevalence of lifetime smoking among medical college students(r=-0.64),while the scores of smoking-related knowledge and attitude showed a positive correlation with family socio-economic status,with the r values of 0.071 and 0.077,respectively.Male,parental smoking behavior,roommates' smoking behavior,close friends' smoking behavior,low family socio-economic status and negative attitude to refuse smoking were the risk factors of attempting smoking;male,roommates' smoking behavior,close friends' smoking behavior and negative attitudes to refuse smoking were also the risk factors of current smoking.Conclusion Our study indicates that family socio-economic status is related with smoking behaviors among medical college students,and the positive influence of family members and friends should be considered to prevent smoking among medical college students.