In surgery for colorectal cancer, a tendency of immune suppression was noted as seen in surgery for other types of gastro-intestinal cancer. This tendency was also found in the biological response, and it was related to the operative procedures and insults for rectal cancer. The degree of immunosuppression was milder in patients who underwent procedures that preserve the natural sphincter than in those who underwent colostomy. It is important for surgeons to avoid postoperative immunosuppression in order to prevent recurrence and improve prognosis. Given similar degrees of operative insult and stage of cancer, an operative procedure which causes as little immunosuppression as possible should be selected.