Keywords： hemodialysis, acquired factor V inhibitor, cerebral hemorrhage 〈Abstract〉 In X 3 years, a woman in her 70s was started on hemodialysis. Her PT and APTT were 11 and 24 sec, respectively, at that time. Nafamostat mesylate had been used during dialysis as of October X 1, after she developed gastric antral vascular ectasia. She was treated with antimicrobial agents for fever and cough in February X, but did not improve. She was consequently admitted to our facility. Aside from pneumonia, abnormal coagulation was observed (PT： 54 sec, APTT： 215 sec). Coagulation factor V activity was significantly reduced, and factor V inhibitor and antiFV autoantibodies were detected in the blood, indicating the presence of acquired factor V inhibitor. The patient showed a right temporal lobe hemorrhage on the 33rd day of hospitalization, and 10 units of platelet concentrate were transfused. On the 34th day, oral prednisolone at 20 mg/day was initiated. On the