Background: Perioperative transfusion of red blood cell (RBC) may cause adverse effects. Bloodless-cardiac surgery has been spotlighted to avoid those problems. Off pump coronary artery bypass (OPCAB) surgery can decrease the transfusion. However, the risk factors of transfusions in OPCAB have not been investigated properly. Materials and Methods: One hundred and thirteen patients (male:female=35:78, mean age=$66.7{pm}9.9$ years) who received isolated OPCAB were retrospectively analyzed from March 2006 to September 2007. The threshold of RBC transfusion was 28.0% of hematocrit. Bilateral internal thoracic arteries graft were used for 99 patients (87.6%). One hundred and three (91.1%) and 35 patients (31.5%) took aspirin and clopidogrel just before surgery. Results: Sixty-five patients (47.5%) received the RBC transfusion (mean $2.2{pm}3.2$ units). Mortality and major complications were not different between transfusion and no-transfusion group. But, ventilator support time, intensive care unit stay and hospitalization period had been reduced in no-transfusion group (p<0.05). In multivariate analysis, patients risk factors for RBC transfusion were preoperative low hematocrit (<37.5%) and clopidogrel medication. Surgical risk factors were longer graft harvesting time (<75 minutes) and total operation time (<5.5 hours, p <0.05). Conclusion: We performed the transfusion according to transfusion guideline; over 40% cases could conduct the OPCAB without transfusion. There were no differences in major clinical results between transfusion and non-transfusion group. In addition, when used together with accurate understanding of transfusion risk factors, it is expected to increase the proportion of patients that do not undergo transfusions.