Coronary artery bypass grafting surgery (CABG) is an important approach to treating coronary heart disease. However, patients undergoing open heart surgery are at risk of postoperative complications. Cigarette smoking is one of the preoperative risk factors that may increase postoperative complications. Studies show that early mobilization intervention may reduce these complications and improve functional capacity, but the impact of smoking on early outcomes after CABG has been controversial for the past two decades. This quasi-experimental study explored the effects of early mobilization on functional capacity among patients with different smoking histories undergoing CABG. The study involved 51 participants who underwent CABG surgery, divided into three groups: current smokers, former smokers, and non-smokers (n=17 each). A day before surgery, all groups underwent a six-minute walking test (6MWT). Every participant received the same intervention after surgery, including deep breathing exercises, an upper limb range of motion assessment, an incentive spirometer, and walking with and without assistance. Five days postoperatively, all outcomes – including the 6MWT, length of stay (LOS) in the ICU, and postoperative pulmonary complications – were assessed, and the 6MWT was repeated. There was a reduced functional capacity after CABG in ex-smokers (215.8±102 m) and current smokers (272.7±97m) compared to non-smokers (298.5±97.1m) in terms of 6MWT (p<0.05). Current smokers were more likely to have atelectasis after CABG than ex-smokers (76.5% vs. 52.9%), with non-smokers being the least likely to have atelectasis among the three groups (29.4%, p<0.05). Additionally, current smokers required longer ventilator support post-CABG (11.9±7.3 hours) compared to ex-smokers (8.3±4.3 hours) and non-smokers (7±2.5 hours, p<0.01). Smoking status significantly impacts functional capacity reduction after CABG, with current smokers being more susceptible to prolonged ventilator use and atelectasis.