Introduction: The aim of our study is to determine whether there is a relationship between preoperatively measured vitamin D, postoperative development of AF and early adverse events and vitamin D in patients with isolated off-pump coronary artery bypass. Method: Fifty five consecutive patients who underwent off-pump coronary bypass in our hospital were included. Patients were divided into two groups group 1 (n = 44) as patients who developed AF at any time within the first five days after the operation.and group 2 non-AF (n = 11). Two groups were examined in terms of preoperative blood vitamin D levels, postoperative AF and postoperative complications. Results: There was no significant difference between the two groups in terms of preoperative vitamin D values (P = 0.850). In terms of postoperative complications, there was no difference between respiratory problem, pleural effusion, wound infection, stroke, dialysis due to kidney failure and mortality (p> 0.05). In addition, no difference was found between vitamin D and postoperative complications. Conclusion: In our study for the first time in the literature, it was examined whether there was a relationship between preoperative vitamin D levels and AF development after off-pump coronary bypass. In our study, which was about 1 year and involving all seasons, there was no significant relationship between vitamin D and postoperative AF.