Objectives: The aim of this prospective randomized study was to evaluate the effects of platelet-rich plasma (PRP) and fresh frozen plasma (FFP) on homeostasis after cardiopulmonary bypass surgery in Mitral valve replacement patients.Design: Thirty patients were allocated into two groups, each of which contains fifteen patients receiving either platelet-rich plasma or fresh frozen plasma. Results: Platelet count, adenosine diphosphate (ADP) maximum aggregation rate and clotting Factor VIII were greater in the platelet-rich plasma group (n=15) than in the fresh frozen plasma group (n=15). Blood loss after heparin neutralization was less in the PRP group than in the FFP group. Blood loss from heparin neutralization to 12 hours after surgery was correlated with platelet count, fibrinogen, Factor VIII and ADP aggregation rate. The amount of homologous blood transfusion which required was less in the platelet-rich plasma group. Conclusions: We concluded that the use of platelet-rich plasma improves homeostasis after cardiopulmonary bypass, and may be better for cardiac surgery to be performed with platelet-rich plasma than fresh frozen plasma.