The prevalence of smoking in developing countries is known as a significant public health problem, and it is correlated with different demographic and socio-economic factors. This study aimed to determine the environmental and economical related factors of smoking among Iranian adults aged 35 to 70 years. The study sample consisted of 20,152 of Ardabil population aged 35-70 years which was enrolled in the PERSIAN cohort study. Smoking status during the last year was defined as dependent variable and demographic and socio-economic factors considered as independent variables. To identify the main socio-economic factors affecting the smoking prevalence in Ardabil, multivariable logistic regression was used. The prevalence of smoking was 16.1 (95%, CI 15.5-16.4) in this study, where the prevalence of smoking was for men and women 33.4% and 1.4%, respectively. The prevalence of smoking had significant association with old age (2.05, 95% CI, 1.66 to 2.53), male gender (45.15, 95% CI, 37.14 to 54.89), being married (2.60, 95% CI, 1.51 to 4.46), having cardiovascular disease (1.54, 95% CI, 1.32 to 1.79), and negative association with illiteracy (0.50, 95% CI, 0.40 to 0.64), being obese (0.83, 95% CI, 0.73 to 0.94), and lower socio-economic status (0.74, 95% CI, 0.64 to 0.84). The study showed that the prevalence of smoking in Ardabil is higher than many other countries, and different factors, especially socio-economic status, have an association with the prevalence. There are deep needs to policies and regulations such as increasing the taxation on a cigarette to reduce the negative effect of smoking in Iran.