Objective To determine whether the CD133+ cancer stem cells lie in circumferential resection margin of rectal cancer,and to explore the relationship between CD133+ cancer stem cells and prognosis of rectal cancer.Methods The circumferential resection margin of rectal cancer was cut,one half of the tissue was stained HE for microscope observation.Both groups were labeled CD133 by immunohistochemistry.The tissues with positive circumferential resection margin were classified as experimental group,otherwise the control group.Another half was made into single cell suspension and used to detect CD133+ cancer stem cells by flow cytometry.The relapse of patients in the experimental group was following-up.Results Two cases were positive by immunohistochemistry in the experimental group (28 cases),showed that CD133+ cancer stem cells were in circumferential resection margin,but there was not marked difference compared with the control group (72 cases were all negative) (P =0.076).CD133+ cancer stem cells can be detected by flow cytometry,and the expression was higher in experimental group than that in the control group (5.19 ％ and 0.56 ％,Z =-7.739,P ＜ 0.01).In experimental group,the expression of CD133+ cancer stem cells in circumferential resection margin of relapse patients was significantly higher than that in patients without relapse,the difference was statistically significant [(6.57±1.72) ％ and (4.77±1.33) ％,t =3.038,P ＜ 0.05].Spearman rank correlation analysis showed that the proportion of CD133+ cancer stem cells in the experimental group was positively correlated with relapse (rs =0.473,P ＜ 0.05).Conclusion There are CD133 + cancer stem cells within circumferential resection margin of rectal cancer,and the expression of CD133+ cancer stem cells in experimental group is correlated with the postoperative recurrence.