While several studies of smoking behaviors in rural-to-urban Chinese migrants exist, none to our knowledge have focused on factory workers, estimated to represent between 10% and 20% of China's total rural-to-urban migratory population. This paper assesses factors associated with smoking behavior among rural-to-urban migrant factory workers in Shenzhen, China. A cross-sectional survey of migrant workers from 44 randomly selected factories in Shenzhen, China. Participants were migrant factory workers aged 16-59 years and holding nonlocal household registration. The main outcome measures were demographic, migration-related, and behavioral factors associated with smoking status. Four thousand and eighty-eight completed questionnaires were obtained (response rate 95.5%). Overall smoking prevalence (including occasional, daily, and heavy daily smoking) was 19.1%. The prevalence of daily smoking (including heavy daily smoking) was higher in men (27.3%) than women (0.7%). These rates are significantly lower than national smoking rates (59.5% in men, 3.7% in women) and rates found in a similar study. A high-risk group of men who smoke heavily and consume alcohol frequently was identified. Longer working hours and less rest were associated with higher rates of smoking. Frequent Internet use and lack of insurance were associated with lifetime smoking. Gender-adjusted models showed that poorer mental health and an accumulated working time in Shenzhen of 2-3 years increased female workers' likelihood of smoking. Migrant factory workers in Shenzhen had lower rates of smoking than other population groups in China. The identification of risk factors for heavy smoking may help to effectively target health promotion interventions.