【Abstract】Objective To identify the effect of Nacetyl cysteine (NAC) in reducing early reperfusion injury and acute oxidative stress in patients undergoing coronary artery bypass grafting(CABG). Methods In this clinical randomized doubleblind controlled trial, 90 patients (American Society of Anesthesiolosts ⅡⅢ,cardiac function grade ⅡⅢ) underwent elective CABG were enrolled. Patients were randomly divided into the control group (group C,n=45) and the NAC group (group N,n=45). Patients in group N received NAC 2400mg for five consecutive days before surgery, while patients in group C received normal saline. Blood samples were withdrawn from arterial line, before the induction of anesthesia (T0), at the end of the surgery(T1),1 hour after the surgery(T2), 6 hour after the surgery (T3) and 12 hour after the surgery(T4). The blood samples were analyzed for cTnI, Myo, CKMbmass, lactate, MDA and TNFα levels, time to extubation, days of mechanical ventilation, length of ICU and hospital stay.Results Compared with group C, cTnI, myoglobin, CK MB, lactic acid and TNF α in group n were significantly lower at t  1  to t  4  time points (all P＜005), and MDA in group N was significantly lower at t  3  to t  4  time points (all P＜005). Compared with group C, the extubation time and mechanical ventilation time of group n were significantly reduced (P＜005), but there was no significant difference in ICU stay and hospital stay (P＞005). Conclusion Preoperative use of NAC can reduce myocardial reperfusion injury caused by early oxidative stress in patients with CABG.