Abstract: Objective:This study aims to determine the suitable cell line to be used in isolating cancer stem cells by comparing the characteristics of tumor stem cells in renal cell carcinoma cell lines SN12C and 786 -O. Methods:The rate of sphere formation in SN12C and 786 -O cells was determined in serum-free medium (SFM). The expression levels of CD 133 , CD 44, Nanog, and Oct 3/4 were investi -gated through flow cytometry. Moreover, the tumorigenicity of spheroid cell that originated from SN 12C and 786 -O cells was investi -gated in vivo by using a tumor model.Results: The average time of sphere formation in SFM was shorter in SN12C than in 786 - O ( 5 days vs . 7 days). Moreover, the expression levels of CD133 , CD 44, Nanog, and Oct3/4 in SN12C and 786 - O significantly differed ( P< 0. 05). When transplanted in nude mice, 786 -O spheres were less tumorigenic than SN12C spheres.Conclusion: SN12C spheres possess the main defining characteristics of renal cancer stem cell; thus, SN 12C is the more suitable cell line to be used to isolate cancer stem cells compared with786 -O.