During the course of anesthetic administration, appreciate volume of nitrous oxide can move into closed gas spaces. The use of nitrous oxide during abdominal surgery may cause distension of the intestine and make difficulty in operating procedure. We studied 29 patients undergoing elective colorectal surgery and they were classified into two groups -N2O group and Air group, N2O group was administered with air-oxygen-enflurane before peritoneal opening and administered with N2O- oxygen-enflurane after peritoneal opening. Air group was administered with air-oxygen-enflurane throughout the surgery. We measured N2O concentration in the terminal ileum, the degree of distension in the small and large intestine during anesthesia, and the time of postoperative flatulence and feces passage. The N2O concentration in the intestine increased throughout the time course in N2O group. The distension score of the small and large bowel had a tendency to increase in N2O group. There were no significant differences between the two groups in postoperative bowel motility. These results suggest that a long-term N2O administration in patients undergoing colorectal surgery may interfere surgical conditions of the intestine because of the bowel distension.