To avoid cerebral hypoxia caused by the imbalance between cerebral oxygen supply and consumption, regional cerebral oxygenation of patients need to be monitored at real time during cardiopulmonary bypass (CPB) surgery, and the physiological parameters can be regulated and emergent treatment can be used according to it. Using the near infrared (NIR) instrument developed by our group, cerebral oxygenation of the patients under cardiac surgery was monitored. The instrument consists of a two-wavelength near infrared light source and two near infrared detectors. Hemoglobin concentration changes of regional cerebral tissue were calculated, and by steady-state spatially resolved spectroscopy (SRS) algorithm, regional cerebral oxygen saturation (rSO2) was also calculated. Physiological parameters of patients, such as mixed venous oxygen saturation (SvO2), were measured by another monitor during CPB. Hemoglobin concentration changes were easily disturbed, but the anti-disturbance ability of rSO2 was good. The value of rSO2 could be detected all over the surgeries, but SvO2 could be detected only during CPB. There were positive correlations between rSO2 and SvO2 in most of the patients, but the correlation coefficients were not very high. This was because SvO2 reflects the saturation of the main venous, but rSO2 reflects regional cerebral oxygenation. So the physiological meaning of rSO2 and SvO2 is different. The results indicate that cerebral oxygenation of patients can be reflected by rSO2 during CPB, while only monitoring SvO2 is not enough.