Background: China has become the world's largest producer and consumer of tobacco and lung cancer is China's leading cause of cancer deaths. The large majority of Chinese smokers are men. Tobacco consumption is of particular concern among China's internal floating (or migrant) population, which has become a permanent feature of Chinese society, because this population is very large (over 100 million persons) and it has a high prevalence of smoking. Considering additionally that like the general population of China, the smoking prevalence rate of women from this group is quite low, we therefore aimed to explore smoking-related knowledge, attitudes and behaviours among male smokers in the floating population to help inform the development of effective smoking cessation interventions in this important target group in China. Methods: We interviewed 39 floating population male smokers in six focus groups and performed a qualitative content analysis of the interviews. Results: Most participants knew that smoking is risky to health but they knew little about why. Habit and social participation were key drivers of smoking. Smoking was regarded as a core component of their identity by the urban residents. Some participants had tried to stop smoking but none reported having ever been educated about smoking. Conclusions: Smoking cessation interventions for China's male floating population would need to incorporate comprehensive education and information about why smoking is dangerous and the benefits of stopping.