Background: We aimed to determine the relationship between HbA1c levels and the development of postoperative atrial fibrillation (PoAF) . Methods: 288 patients diagnosed with diabet and undergoing on-pump coronary bypass were included in the study. Those with serum HbA1c levels between 5.5-7.0% were defined as Group 1, those with serum HbA1c levels between 7.1-8.9% were defined as group 2, while those with serum HbA1c levels 9.0% and above formed Group 3. Data between groups were compared. The predictive values of the independent variables for the development of PoAF were measured. Results: We did not found difference between groups in terms of development PoAF (p=0.170). Presence of hypertension was determined as an independent predictor for the development of PoAF (p=0.003) but not HbA1c levels (p=0.134). There was 50.5% sensitivity and 61.1% specificity for HbA1c values of 9.06% and above to predict PoAF (AUC: 0.571, p=0.049) Conclusions: HbA1c levels were not an independent predictor of PoAF development. However, we think that high HbA1c levels may be a risk factor for the development of PoAF.