A case of Hemophilia B, 20y., had valgus osteotomy of the left femoral neck. The preliminary replacement with PPSB was revealed not to introduce inhibitor and no other abnormal enzyme activity was found except for the slight disturbance of liver function. The operation was gotten ready with injection of 10 vials PPSB and performed smoothly in 2 hours with 340ml of blood loss. PPSB administration was scheduled in a daily dosis of 20 vials divided in twice. But at the third postoperative day, large hematoma concreted in the femoral region with severe pain and was followed by the massive bleeding from the wound. Coagulation tests revealed decreased platelet count, prolonged.PTT and prothrombin time, decreased fibrinogen and increased FDP. The concentration of F.IX was not lifted so high as expected after the injection of 10 vials of PPSB, which, together with the above mentioned changes of coagulation factors, suggested the developement of defibrination syndrome.The replacement of PPSB was continued together with 10,000 U of heparin and 800ml of fresh plasma per day. At the 7th postoperative day, the coagulation findings of defibrination syndrome were gradually improved, bleeding decreased and F. IX level elevated as could be calculated. The administration of PPSB was diminished and discontinued at 29th day and of heparin at 45th day without any bleeding complication thereafter.