Postoperative fatal pulmonary embolism caused thrombi from low extremity deep veins of patients after abdominal operation remains a major cause of death. Blood biorheology in 34 patients having pelvic operation and 41 patients having non-pelvic operation was studied. Blood viscosity was significantly higher in pelvic operation than in non-pelvic operation. The low extremity venous blood viscosity was significantly higher than the upper extremity venous blood viscosity. These suggest that hyperviscosity status and hypercogulable of low extremity veins may be an important cause that deep venous thrombogensis occurs prone to the low extremities in patients with pelvic operation.