Objectives: The purpose of this study was to identify any influence of socioeconomic status on smoking and smoking cessation in a situation where genetic factors are controlled. Methods: The sample for this study was 2502 members of the twins and families cohort who participated in the Korean Healthy Twins Study from 2005 to 2009. Groups of brothers or sisters, including twins and fraternal twins, were compared in terms of smoking and smoking cessation behaviors according to differences in socioeconomic status and gender. Results: In a situation with complete control of genetic factors, results showed that the daily smoking amount, cumulative smoking amount, and dependence on nicotine decreased with higher-status occupations, and the rate of smoking and amount of cumulative smoking decreased with higher levels of education. Regarding smoking cessation behavior, a higher level of education was associated with a lower smoking cessation rate, and no significant gender differences were found. Conclusions: Environmental factors had a stronger influence on smoking behavior than did genetic factors. Genetic factors had greater influence on smoking cessation than did environmental factors; however, this requires verification in further studies.