Ｏｂｊｅｃｔｉｖｅ　To evaluate the effects of hemoglobin(Hb) concentrations during cardiopulmonary bypass (CPB) on postoperative cognitive dysfunction (POCD) in patients.　Methods　One hundred and eight patients underwent cardiopulmonary bypass were enrolled in this study. According to their Hb concentrations, patients were divided into 3 groups. Patients with normal levels of Hb, 90-110, 60-90 g/L Hb were respectively assigned into groupⅠ, group Ⅱ and group Ⅲ. The patients′ Hb concentration 1 day before the surgery, during cardiopulmonary bypass, 1, 2, 3, 4 and 7 days after the surgery were measured. The cerebral oxygen saturation (rSO2) was also assayed during CPB. The score of the neuropsychological test on the day before surgery and the seventh day after surgery were recorded. Whether Hb concentration and rSO2 levels affect the incidence of postoperative cognitive function was analyzed.　Results　Among three groups, no significant difference was found in basic and operative information, and the score of the neuropsychological test on one day before surgery(P>0.05). The neuropsychological scores at the seventh day after surgery were lower in group Ⅲ compared with groupⅠ(P<0.05). The incidence of POCD was higher in group Ⅱ and group Ⅲ than that in groupⅠ(P<0.05). Compared with groupⅠ, the rSO2 mean and rSO2 min were lower in group Ⅱ and Ⅲ on the seventh day after surgery(P<0.05).　Conclusions　Patients with anemia are susceptible to POCD, which might be related to decreased cerebral oxygen saturation. Hb concentration may be an independent risk factor for POCD.