We could performed the safe operation for thoracoabdominal aortic aneurysm complicated with pre-DIC. A diagnosis of pre-DIC was made by laboratory data. Low heparin pretreatment was performed for the short term because we presumed the cause for pre-DIC was thromboses in aneurysm. That treatment was effective for the temporal remission of pre-DIC. In addition, during partial ECC low heparin (1 mg/kg) and nafamostat mesilate (2 mg/kg/h) were used. As a result, during and after the operation blood loss was a little. In summary heparin pretreatment is useful therapy for DIC and pre-DIC in aortic aneurysm patients.