Pain and cigarette smoking are very common in heroin-dependent patients (HDPs) receiving methadone maintenance treatment (MMT) and both have substantial negative effects on HDPs' physical and mental health. Nevertheless, very few studies have assessed the relationship between the two in HDPs. This study examined the association between pain intensity and smoking in Chinese methadone-maintained HDPs. A total of 603 HDPs were consecutively recruited from three MMT clinics in Wuhan, China, and administered with a socio-demographic and drug use questionnaire, a smoking questionnaire concerning average number of cigarettes smoked daily and Heaviness of Smoking Index, and Zung's Self-rating Depression Scale. We used a five-point Verbal Rating Scale to rate the intensity of pain. To determine whether pain's associations with smoking and nicotine dependence were independent, an analysis of covariance was adopted to control for the potential confounding effects of socio-demographic variables, drug use characteristics, and depressive symptoms. Net of potential confounders, in methadone-maintained HDPs, pain intensity was significantly higher in smoker than non-smokers (F = 11.836, P = 0.002) but the pain intensity did not differ significantly across patients with various levels of cigarette consumption (F = 1.992, P = 0.137), while the pain intensity significantly differed across patients with different levels of nicotine dependence (F = 3.252, P = 0.013). Pain is significantly associated with smoking in HDPs receiving MMT, this phenomenon may be explained by the association between nicotine dependence and pain.