Ｏｂｊｅｃｔｉｖｅ　To explore the effects of dexmedetomidine(Dex) on expressions of caspase-3 and Bax in hippocampus tissues of aged mice after surgery and postoperative cognitive dysfunction(POCD).　Methods　A total of 105 aged Kunming mice were randomly divided into 4 groups: control group(C group, n=15) that received no anesthesia and surgery, anesthesia group (A group, n=30) that received 1.5% to 2% consecutive isoflurane inhalation for 60 min combined with intraperitoneal injection of 100 mg/kg ketamine on 1 d(A1 group) and 3 d(A3 group) after surgery, splenectomy group (P group, n=30) that undergoing splenectomy under the same anesthesia as in A group named P1 group and P3 group, intervention group(D group, n=30) that received intraperitoneal injection of Dex of 15 μg/kg and 25 μg/kg (15 mice for each dose as D15, D25) for 30 min before anesthesia and surgery. Y-maze experiments were conducted on 1 d and 3 d after surgery to investigate the neuro?蛳behavioral differences(Y?蛳maze experiments were conducted on 3 d after surgery for D group). The frequencies of training of each group were recorded. The protein expression and positive cells of Bax and caspase?蛳3 in hippocampus tissues were detected by Western blot and Immunohistochemistry assay respectively.　Results　Compared to C group(27±8), on day 1 after surgery in anesthesia group(50±10), and on day 1 and 3 after surgery in P group[(70±15), (65±16)], training times were increased in the training frequencies(P<0.01, P<0.05). No significant difference was seen between D groups(D15, D25 group) and control group(P>0.05). Compared with P3 group(65±16), the training frequency of D25 group (29±6) was significantly different(P<0.05). Compared with the C group, caspase-3 and Bax protein expression and positive cells in hippocampus tissues in anesthesia and splenectomized group were significantly increased on 1 d and 3 d after surgery(P<0.01, P<0.05), especially in splenectomy group. The differences between the intervention groups(D15, D25) and control group were not statistically significant on 3 d after surgery(P>0.05). Compared with the splenectomy group 3 d after surgery, Caspase-3 and Bax protein expression and positive cells in hippocampus tissues in intervention groups(D15, D25) were significantly decreased 3 d after surgery(P<0.01, P<0.05).　Conclusions　Pretreatment with Dex can greatly reduce Caspase 3 and Bax protein expression and their positive cells in hippocampus tissues of mice and the improvement of POCD of mice is relevant to decrease expressions of caspase-3 and Bax.