Abstract: Objective : To evaluate the characteristics of circumferential margin infiltration in middle and (or) lowerrectal cancer, to investigate the pathological basis for the prognosis of rectal cancer, to validate circumferen-tial margin involvement (CMI) as a very important factor in reducing postoperative recurrence, and to providea theoretical foundation for the selection of specific parameters for clinical diagnosis and treatment of rectalcancer. Methods : We analyzed the pathological features of 41 tissue samples obtained from patients with mid-dle or lower rectal cancer who underwent surgery with the principles of total mesorectal excision (TME) duringNovember 2006 and July 2007. Results : The positive rate of CMI was 21.95% (9/41). The positive rates ofmoderately and well differentiated CMI were 16.67% (1/6) and 8% (2/25), respectively, while the positive rateof poorly differentiated infiltration was 60% (6/10) (P<0.05). The positive rate of CMI was lower in moderatelyand well differentiated groups than in the poorly differentiated group. The positive rate of CMI was 46.15% (6/13) in the specimens whose lower edge was less than 5 cm to the dentate line and 10.71% (3/28) in the speci-mens whose lower edge was not less than 5 cm, with a significant difference (P<0.05). No significant correla-tion was found between circumferential resection margin and other clinicopathologic features such as gender,age, tumor infiltration, lymph node metastasis, pathological type or surgical method (P>0.05). Conclusion : Cir-cumferential margin infiltration in patients with rectal cancer can be observed in pathological large slices.Pathological large slices can help accurately identify the TNM stage of rectal cancer and select correspondingclinical treatment. Examination of pathological large slices should be a routine procedure after surgery for pa-tients with rectal cancer. Patients with circumferential margin infiltration should be treated with routine radio-therapy and chemotherapy after surgery to reduce the possibility of local tumor recurrence.