Ｏｂｊｅｃｔｉｖｅ　To evaluate the effect of dexmedetomidine (Dex) on the prevention and treatment of postoperative cognitive dysfunction (POCD) in elderly patients.　Methods　The study includes patients (≥ 65 years) classified as ASA class Ⅱ or Ⅲ who underwent elective gastrointestinal surgery. All enrolled patients were randomly divided into control group (group C, n=33) and Dex group (group D, n=32). The group D and group C were respectively given 1 μg·kg-1·h-1 Dex and 0.9% NaCl 10 min before surgery. All patients received intravenous anesthesia to maintain the BIS value between 45 and 65. Recored the general condition of the patient, the dosage of remifentanil and propofol and hemodynamic changes before Injection of Dex(T0), 10 min after administration (T1), 20 min after administration(T2) and at the end of surgery(T3). POCD was evaluated with the neuropsychological testing.　Results　Total doses of remifentanil and propofol in group D were significantly reduced in comparison with group C(P<0.05). HR, SBP, and DBP at T1 were higher than T0 in group C (P<0.05), while HR, SBP, and DBP at T2 were lower than T0 in group D(P<0.05). HR, SBP and DBP in group D were lower than group C at T1 and T2(P<0.05). The incidence of POCD in group C was 30.3%(10/33), significantly higher than that in group D(6.3%, 2/32, P<0.05).　Conclusions　Dex can reduce total doses of remifentanil for anesthesia and the incidence of POCD during elective gastrointestinal surgery, and stabilize hemodynamics.