Objective To observe the effect of different surgical types on the cognitive function in elderly patients with rectal cancer after surgery. Methods 80 patients undergoing elective surgery in our hospital were selected as study subjects. According to different surgical types, the patients were divided into the open group and the laparoscopic group, 40 cases in each group. The general data and general situation during surgery were observed. The arterial partial pressure of carbon dioxide (PaCO2), arterial venous oxygen content difference and cerebral oxygen extraction rate were compared between the two groups at 5 min before surgery, 30 min after pneumoperitoneum and 1 h after pneumoperitoneum. Levels of serum S100β, scores of Mini Mental State Examination (MMSE) and the incidence rates of POCD at different time points before and after surgery were compared. Results Compared with the laparoscopic group, the surgical time of the open group was significantly short (t=2.406, P＜0.05), while the blood loss and dosage of fentanyl during surgery were significantly large (t=2.936 and 4.474, P＜0.05). The PaCO2 in laparoscopic group at 30 min and 1h after pneumoperitoneum was significantly higher than that in open group (t=2.771, 6.486, P＜0.05), while the arterial venous oxygen content differences and cerebral oxygen extraction rates were significantly lower than those in the control group (t=3.875, 3.655, 3.091, 2.299, P＜005). 1d and 3d after surgery, levels of serum S100β in the open group were significantly lower than those in the laparoscopic group (t=3.406, 4.955, 2.868, P＜0.05) while the MMSE scores were significantly higher than those in the laparoscopic group (t=8.955, 8.912, P＜0.05). The incidence rates of POCD in the open group in 1d and 3d after surgery were significantly lower than those in the laparoscopic group (x2=4.242, 4.804, P＜0.05). There was no significant difference in the incidence rate of adverse reactions between the two groups (x2=0.012, P＞0.05). Conclusion Under the same anesthesia, the effect of open surgery on the mental status and cognitive function in elderly patients is less than that of laparoscopic surgery.