To estimate the accuracy of regional cerebral oxygen saturation (rSO2) in predicting postoperative cognitive dysfunction (POCD) for patients undergoing total hip arthroplasty, 46 patients aged more than 50years old were enrolled. We measured the patients’ cognitive function by using a battery of six neuropsychological tests before surgery and then 7days after surgery again. rSO2 was continuously monitored by near-infrared spectroscopy during surgery. POCD was present in 9 (19.6%) patients 1week after surgery. Logistic regression analysis showed that increasing age [OR=1.224, P=0.035] and maximum percentage drop in rSO2 (rSO2%max) [OR=1.618, P=0.011] were significant risk factors for POCD. The area under the receiver operating characteristic curve of rSO2%max was 0.833 [95% confidence interval (CI) 0.615–1.051] at cutoff value of 11%. The specificity and sensitivity of rSO2%max >11% in predicting POCD were 77.8% and 86.5%, respectively. rSO2%max more than 11% was a potential predictor for POCD.