Abstract: Objective To study the influence of preoperative chemo-radiotherapy on the curative effect of low rectal cancer patients, postoperative complications and T lymphocytes. Methods A total of 108 patients with T3-T4 low rectal cancer were divided into the preoperative chemo-radiotherapy group (53 cases) and simple operation group (55 cases), and patients in chemo-radiotherapy group received 3 weeks chemo-radiotherapy before operation. The duration of operation, bleeding volume, anal preservation rate after treatment and postoperative complication of patients were compared between two groups, and the level of serum T lymphocyte subsets in two groups before and after operation was also detected by flow cytometry. Results There were no significant difference on duration of operation, intraoperative bleeding volume and postoperative complication incidence between two groups (P>0.05), but the anal preservation rate of in chemo-radiotherapy group was significantly higher than that of the simple operation group （P<0.05）. The level of serum T lymphocyte subsets before the treatment had no significant difference between the chemo-radiotherapy group and simple operation group (P>0.05). The T lymphocytes showed significant difference between the chemo-radiotherapy group and simple operation group 1 week after the chemo-radiotherapy (P<0.05). The percentage of CD＋4 lymphocytes and the CD＋4/CD＋8 ratio in chemo-radiotherapy group increased 3 months after the operation, showing significant difference compared with the results before and 1 week after the chemo-radiotherapy (P<0.05), but showing no significant difference compared with the results of simple operation group. Conclusion Preoperative chemo-radiotherapy can significantly improve the anal preservation rate without increasing the difficulty of operation and the incidence of postoperative complications. It can be adopted as a safe, effective and reasonable adjuvant therapy without influence on the immune function.