Bleeding is a common complication of cardiac surgery, accounting for a significant proportion of the total transfusions performed in the United States and Europe. The relationship between platelet reactivity, bleeding, and other adverse events after coronary artery bypass graft surgery (CABGS) has been incompletely characterized. This study investigated the relationship between platelet reactivity and bleeding as a clinical outcome after successful CABGS. A total of 238 patients who underwent CABGS were retrospectively followed for postoperative bleeding. Platelet reactivity unit (PRU) values for all patients were obtained preoperatively to assess the platelet reactivity. The data showed that a range of 180–200 PRU suggests the likelihood of bleeding after CABGS (P = 0.004), with a statistically significant association only for dual antiplatelet therapy with aspirin and clopidogrel. In conclusion, by using PRU values as a method to assess platelet reactivity and antiplatelet responsiveness, our findings suggest that it may be possible to stratify patients undergoing CABGS for the risk of postoperative bleeding particularly patients on dual antiplatelet therapy.