A 73-year-old man receiving anticoagulants (warfarin potassium) orally with a history of prosthetic heart valve replacement was struck by a truck. When admitting to the hospital, he complained of lumbago with laboratory findings of anemia and prolongation of prothrombin times. Twenty-two hours after the accident, he died suddenly in the hospital and forensic autopsy was performed 9 hours after his death. Autopsy findings revealed marked subcutaneous and intramuscular hematoma in the lumbar and gluteal region and anemic change of viscera. Furthermore, 854 ng/ml of warfarin which was well accordance with the therapeutic levels was detected in the serum obtained from cadaver by using gas chromatography-mass spectrometry. Therefore, we concluded that the man had died of hemorrhagic shock caused by the force acting to the lumbar region accompanied by the influence of anticoagulant action of warfarin. To our knowledge, this is the first report to detect the warfarin from cadaver's serum. In dealing with the unnatural death of the patient receiving the anticoagulants, it is valuable to survey the medications and detect the presence of anticoagulants in cadaver.