Abstract: Objective To evaluate the effects of dexmedetomidine on respiratory function in patients undergoing laparoscopic radical resection for colorectal cancer. Methods A total of 60 patients (aged 60-80 years old, ASA grade Ⅰ—Ⅱ) who underwent laparoscopic radical resection for colorectal cancer in the Affiliated Hospital of Xuzhou Medical University from December 2016 to December 2017 were enrolled. According to the random number table method, they were randomly divided into two groups (n=30): a control (N) group and a dexmedetomidine (D) group. The D group received infusion of 0.5 μg/kg dexmedetomidine 10 min before anesthesia induction, followed by continuous pump infusion of dexmedetomidine at 0.4 μg/(kg·h) until 30 min before the end of operation. Meanwhile, the equal volume of normal saline was infused in the N group. Arterial blood samples were taken for blood gas analysis before administration of dexmedetomidine or normal saline (T₀), immediately after pneumoperitoneum was established (T₁), 30 min (T₂) and 60 min (T₃) after pneumoperitoneum was established, at the end of pneumoperitoneum (T₄), and 24 h after extubation (T₅). Then, arterial partial pressure of oxygen (PaO₂) and arterial partial pressure of carbon dioxide (PaCO₂) were recorded at each time point to calculate alveolar-arterial difference (P_A-aO₂), oxygenation index (OI), and respiratory index (RI). Central venous blood samples were taken at T₀, T₄ and T₅ to measure the concentrations of serum interleukin (IL)-6 and tumor necrosis factor (TNF)-α and the incidence of pulmonary complications 72 h after operation. Results Compared with the N group, the D group showed decreases in P_A-aO₂ and RI and increases in OI at T₄, with a reduced incidence of pulmonary complications 72 h after surgery. Conclusions Dexmedetomidine can effectively improve the oxygenation of patients undergoing laparoscopic radical resection for colorectal cancer, decrease inflammation and the incidence of pulmonary complications 72 h after surgery.