A 17-year-old hemophilia A patient with an intracranial bleeding and a high titre of factor VIII inhibitor was treated with repeated infusion of an activated prothrombin complex concentrate (FEIBA). A good effect was achieved clinically, but laboratory tests on 8th day of the treatment revealed no shortening effect on non-activated partial thromboplastin time and on r-value of thrombelastograph. A prolongation of prothrombin time and thrombin time, a decrease in fibrinogen and antithrombin III, and an increase in serum FDP were also observed. These findings returned to normal after FEIBA was stopped. It was suggested that repeated and massive infusion of FEIBA might cause a decrease in natural inhibitors which lead to DIC.