OBJECTIVE： To explore the effects and safety of dexmedetomidine combined with remifentanil on postoperative cognition and hemodynamics in patients underwent colon cancer surgery. METHODS： One hundred undergoing colon cancer surgery in our hospital during Jun. 2013-Apr. 2016 were selected and divided into control group and observation group according to random number table， with 50 cases in each group. Control group was given Remifentanil hydrochloride for injection 2-4 μg/kg for anesthesia induction， with maintenance dose of 0.5-2 μg·kg/min； observation group was treated with Dexmedetomidine hydrochloride for injection 0.5 μg/kg and remifentanil 2-4 μg/kg for anesthesia induction， with maintenance dose of Dexmedetomidine hydrochloride for injection 0.4 μg·kg/h+Remifentanil hydrochloride for injection 0.5-2 μg·kg/min. MMSE score and the incidence of postoperative cognitive dysfunction （POCD） were observed in 2 groups 1， 2， 3 d after surgery， and the occurrence of ADR was recorded. RESULTS： The incidence of POCD in observation group 1， 2， 3 d after surgery were 16.0％， 4.0％， 6.0％， which was significantly higher than 36.0％， 12.0％， 10.0％ of control group， with statistical significance （P＜0.05）. There was no statistical significance in MMSE score between 2 groups 1， 3 d after operation （P＞0.05）. 2 d after surgery， MMSE score of observation group was significantly higher than that of control group， with statistical significance （P＜0.05）. There was no statistical significance in hemodynamic indexes， the incidence of ADR as blood pressure increasing， amyostasia， nausea and vomiting between 2 groups 1， 2， 3 d after surgery （P＞0.05）. CONCLUSIONS： Dexmedetomidine combined with remifentanil can significantly improve postoperative POCD in patients underwent colon cancer surgery and have little effect on hemodynamics with good safety.