Backgrouand: To determine the risk factors and postoperative outcomes of new-onset atrial fibrillation (AF) following beating-heart coronary artery bypass grafting (CABG) surgery. Methods: A total of 458 patients who underwent beating-heart CABG without the use of aortic cross clamping and cardioplegic arrest between January 2011 and January 2015 were included in the study, and they were divided into two groups according to the development of new-onset AF as the AF group (n = 143) and non-AF group (n = 315). Both groups were compared in terms of preoperative clinical features and perioperative data, and the risk factors and postoperative outcomes of AF following beating-heart CABG were determined. Results: The incidence of postoperative AF was 31.2%. Patients in the AF group were significantly older (68.08 ±7.76 vs. 61.76 ±9.83 years, p <=0.001) and had significantly higher use of cardiopulmonary bypass during surgery (69.2% vs. 43.2%, p <=0.001) than the patients in the non-AF group. The patients with AF also had statistically significantly longer lengths of intensive care unit and hospital stay than those without AF (43.79 ±32.39 vs. 30.49 ±33.31 hours, p<=0.001, and 8.20±4.37 vs. 5.77±2.16 days, p <=0.001, respectively). Conclusions: Our study revealed that age and the use of cardiopulmonary bypass during surgery were independent predictors of AF following beating-heart CABG. In addition, postoperative AF was associated with prolonged intensive care unit and hospital stay. Further prospective randomized studies with larger patient series are required to support our research and attain more accurate data.