Abstract: Objective To evaluate the effects of dexmedetomidine on respiratory function of elderly patients underwent radical resection for colorectal cancer under laparoscopy. Methods sixty elderly patients underwent radical resection for colorectal cancer under laparoscopy were randomly divided into control group(group N)and dexmedetomidine group(group D). Thirty cases were included in each group. In group D, a loading dose of dexmedetomidine 0.5 ug/kg was injected into the vein before anesthesia induction, and followed by the dose of 0.4ug/kg/h after anesthesia induction till 30 minutes before the end of operation. The equal volume 0.9% saline was given in group N respectively. Blood samples were taken from radial artery before the using of dexmedetomidine(T0), before the pneumoperitoneum was established(T1), 30 minutes(T2)、60 minutes(T3)after pneumoperitoneum was established, right after the pneumoperitoneum (T4), and 24 hours after operation(T5)to do blood gas analysis. PaO2 and PaCO2 were recorded at each measuring point and calculate alveolar-arterial difference(PA-aO2), Oxygenation index (OI), respiratory index(RI). Central venous blood samples were taken at T0、T4~5 to measure the concentrations of IL-6 and TNF-α in serum and the incidence of postoperative complications of pulmonary complications after three days of operation．Results Compared with group N, PA-aO2, RI and OI increased in group D at time T4, and the incidence of pulmonary complications decreased 72 hours after surgery. Conclusions Intraoperative use of dexmedetomidine can improve oxygenation and respiration function of elderly patients underwent radical resection for colorectal cancer under laparoscopy in anesthesia recovery period