We report two cases of anesthetic management with monitoring by near-infrared spectroscopy in patients with renal cell carcinoma and with adrenal cortical carcinoma, who had tumor thrombus invading into the inferior vena cava. In inferior vena caval reconstruction, extracorporeal circulation such as veno-veno bypass or cardiopulmonary bypass is frequently required. The hemodynamic unstability under extracorporeal circulation may lead to severe cerebral damage, especially in elderly patients. We monitored cerebral oxygenation state during reconstruction of the vena cava by near-infrared spectroscopy. One patient underwent surgery with veno-veno bypass and another patient with partial cardiopulmonary bypass. Oxygenated hemoglobin decreased during extracorporeal circulation, especially during the use of partial cardiopulmonary bypass compared with veno-veno bypass. However, these decreased oxygenated hemoglobin was restored rapidly at the end of extracorporeal circulation. Both patients showed no post-operative neurological complication. We concluded that near-infrared spectroscopy, which is continuous and non-invasive monitoring of cerebral oxygenation status, is one of the useful monitors during extracorporeal circulation.