Limited empirical work has been done to compare the effects that health knowledge and advice from doctors have on smokers’ intentions to quit. This paper examines the association of smokers’ intentions to quit with health knowledge, advice from doctors, and self-perceived health. A sample of 2509 smokers aged 15–69 years old in Ningbo was used from China’s National Health Literacy Surveillance survey, conducted in 2018 and 2019. Respondents were asked whether they agree smoking causes stroke, heart attack, lung cancer; and heart diseases in adults, lung illnesses in children, and lung cancer in adults, by secondhand smoke, respectively. Using the logistic model, we found that knowing that smoking causes stroke and lung cancer more than doubles the odds of one’s intention to quit (OR = 2.705, p < 0.01), the effect of which is much greater than knowing that smoking causes lung cancer only (OR = 1.795, p < 0.01). Doctors’ advice to quit is more important than health knowledge, in terms of predicting smokers’ past cessation behaviours. In addition, smokers’ self-perceived health is negatively associated with their decisions to quit. This paper highlights that more resources should be directed towards training health care providers to advise smokers to quit, which might be more effective than health education alone.