Objective:To isolate and identify cancer stem cells from esophageal cancer cells (ECCs) using cell surface marker p75NTR.Methods: ECCs were cultured from surgically resected ECC specimens; ECC cell lines TE-1 and Eca109 were also cultured.The expression of p75NTR in human ECCs was examined by flow cytometry.p75NTR positive cells were isolated from ECCs using magnetic activated cell sorting (MACS) method.The proliferation,differentiation,and the ability of colony-forming in soft agar of the p75NTR positive cells were observed.The p75NTR positive cells were injected into BALB/c nude mice subcutaneously to observe their tumorigenesis ability.The survival rates of p75NTR positive and negative cells were assessed after treated with chemotherapy drugs to evaluate the resistance of p75NTR positive cells.Results: Six out of the eight cell lines,including SHEC-4,SHEC-6,SHEC-7,SHEC-8,Eca109,and TE-1,were positive of p75NTR ,with the positive rates being 2.71%,0.32%,3.35%,1.13%,2.15%,and 0.45%,respectively.It was showed that p75NTR positive cells possessed higher proliferation ability compared with p75NTR negative cells (P＜0.01).The p75NTR positive cells had higher colony-forming ability in soft agar compared with p75NTR negative cells (P＜0.01).The p75NTR positive cells demonstrated stronger tumorigenesis ability in nude mice. As few as 2 000 SHEC-7 cells could give rise to new tumors in xenotransplantation,with a tumorigenesis ability 50 times as high as that of the p75NTR negative cells.When treated with chemotherapy drugs for 48 h,p75NTR positive cells had significantly higher survival rate than p75NTR negative cells (P<0.05).Conclusion: The p75NTR positive ECCs possess self-renewal,differentiation,and proliferation abilities; they are strongly resistant to chemotherapy drugs,which gives them strong tumorigenesis ability and the characters of tumor stem cells.