Background/aim: The purpose of this study was to examine steroid pretreatment in order to decrease postoperative coagulopathy disorders and bleeding. Materials and methods: In this randomized double-blinded study, the efficacy of low versus high doses of methylprednisolone on the coagulation system and postoperative bleeding was compared in patients who were undergoing cardiac surgery with cardiopulmonary bypass (CPB). The platelet response to agonists, D-dimer concentration, tissue plasminogen activator (tPA), plasminogen activator inhibitor (PAI-1) antigens, and platelet receptors CD42b, CD62P, and CD41a were evaluated. Results: The platelet response to agonists was reduced. The mean concentrations of D-dimer and tPA antigen increased although PAI-1 concentration did not show any significant changes following heparin neutralization. Postoperative expression of CD42b showed no changes in comparison with preoperation values in both groups. There was a significant increase in the expression of CD62P with a methylprednisolone dose of 15 mg/kg, while there was just a slight increase with a dose of 5 mg/kg. CD41a, as a fibrinogen receptor, was increased significantly after CPB in both groups. Significant data were shown in decreasing blood loss with a high dose of methylprednisolone. Conclusion: Methylprednisolone at a dose of 15 mg/kg reduced bleeding, probably by increasing CD62P after heparin neutralization, which can activate platelet activation in favor of better hemostasis.