Post-operative atrial fibrillation (POAF) is considered a common complication after coronary artery bypass surgery (CABG), which is associated with prolonged hospitalization, increased morbidity and even mortality [1]. We investigated the risk factors for POAF and analyzed the relationship between hyperglycemia and atrial fibrillation after CABG. This retrospective study was conducted on 100 patients who were admitted post CABG to critical care department at Benha University Hospital and National Heart Institute. Patients were divided into two groups: Group A included 50 patients who developed POAF and Group B included 50 patients who did not. In this study, we found that history of diabetes mellitus (DM), mean post-operative blood sugar (BS) and maximum post-operative BS were significant (P<0.05) in group A. We also found that post-operative drainage volume was significant in group A. We concluded that post-operative mean BS, maximum BS and post-operative drainage volume were significant risk factors for occurrence of POAF. We should control intensively blood sugar and also decreasing bleeding risks