Abstract: ［Abstract］Objective To investigate the effect of dexmedetomidine on the serum concentrations of S-100β protein and neurone specific enolase （NSE） in elderly patients undergoing surgery. Methods One hundred ASAⅡor Ⅲ patients， aged 65～75 yr with a body mass index of ＜25 kg/m2， scheduled for elective hip joint replacement surgery under general anesthesia， were randomly divided into 2 groups（n =50）: control group （group C） and dexmedetomidine group （group D）. Dexmedetomidine 0.5 μg/kg was infused intravenously over 15 min before anesthesia induction in group D and was maintained 0.4 μg/(kg·h) until 30 min before operation end， while the same volume of normal saline was infused in group C. Anesthesia was induced by iv injection of sufentanil 0.4 μg/kg and propofol 1～2 mg/kg until loss of consciousness. Tracheal intubation was facilitated with 0.6 mg/kg rocuronium bromide and the patients were mechanically ventilated. Anesthesia was maintained with sevoflurane by target controlled inhalation （TCI） （end-tidal concentration set at 1 %~3%） and sufentanil 0.2 μg/(kg·h) in both groups. BIS was maintained at 40～60 during operation.Venous blood samples were obtained for determination of serum concentrations of S-100β protein and NSE before anesthesia （baseline），operation end and at 12h after operation. Patients were sent to Intensive Care Unit when operation end. All the patients were assessed for the development of delirium by experience research staff using Confusion Assessment Method for Intensive Care Unit. The incidence of postoperative delirium within 24h after operation were recorded， and compared between the two groups. Results The serum concentrations of S-100β protein and NSE was significantly increased at T1~2 than at T0 in two groups. The total dose of each anesthetic （propofol， sevoflurane）， the serum concentrations of S-100β protein and NSE， and the incidence of postoperative delirium were significantly lower in group D than in group C（P＜0.05）. Conclusions Dexmedetomidine can reduce the serum concentrations of S-100β protein and NSE， and can also reduce the occurrence of postoperative delirium in elderly patients undergoing hip joint replacement surgery. Dexmedetomidine can provides cerebral protection in elderly patients undergoing surgery.