A 27-yr-old woman who had been taking warfarin for 10 yr after mitral valve replacement became pregnant. After knowing her pregnancy, she received heparinization for nine weeks instead of warfarin, and took oral anticoagulant again. At 24 weeks of gestation, fetal ultrasound and MRI showed a left subdural hematoma, and the pregnancy was terminated. Subdural hematoma was demonstrated on autopsy. Fatal bleeding of the fetus is a rare complication of maternal warfarin medication, occurring mostly in the second or third trimester. There is no alternative regimen available, so that regular monitoring by fetal ultrasound and strict control of warfarin dose with regular measurement of prothrombin time are the best way to prevent intrauterine fetal death due to bleeding.