Background: Atrial fibrillation (AF) is the most common arrhythmia after cardiac surgery. AF leads to longer duration of hospitalization, thromboembolism, and impaired hemodynamics after heart surgery. One of the most important causes of postoperative AF, inflammation, and oxidative stress status. For this reason, it is useful to control the dysrhythmia. Coenzyme Q10 (CoQ10) as an antioxidant that has an important role in reducing the incidence of postoperative AF. The present study aimed at administering CoQ10 as a way to reduce the incidence of post-CABG atrial fibrillation. Methods: In this double-blind randomized controlled trial study, 80 patients with coronary artery disease who underwent coronary artery bypass graft surgery (CABG) in Rajaie Cardiovascular, Medical and Research Center from April to November 2014, randomized are divided into intervention and control groups to receive placebo or CoQ10 The surgical characteristics of the patients in two groups were similar. The intervention group will receive the oral CoQ10 supplement 150 mg/d for 7 days before surgery. After operation two groups were compared regarding important outcomes such as postoperative arrhythmia, intensive care unite (ICU) stay and hospital stay. Atrial arrhythmias are considered significant If more than 10 minutes duration atrial and with a shorter duration of arrhythmia, but with recurrence again. Results: Thirty-eight women and forty-two men with a mean age of 58.37±7.98 years were enrolled in the study in two CoQ10 and placebo groups (each consisting of 40 patients). The incidence of postoperative AF was 45% in the control group to 20% in the intervention group decreased after supplementation (P=0.030). ICU stay and length of in-hospital stay did not significant. The incidence of arrhythmias ventricular tachycardia (VT) and VF in this period was not significant (P=0.865). Conclusion: Q10 supplements have low side effects. Due to the reduction in the incidence of AF in patients after, CABG, these supplements can be recommended for the prevention of AF.