Objective To explore the tumor igenic property of side population cells (SP) from human gallbladder carcinoma cell line GBC-SD. Methods SP and non-SP cells were isolated from GBC-SD staining with Hoechst33342 dye by fluorescence-activated cell sorting (FACS). The soft agar clonal assay and xenograft assay were performed to characterize tumorigenic property of side population cells in vitro and in vivo, respectively. The percentage of SP cells was analyzed by FACS in 5 hu man gallbladder carcinoma specimens. Results The percentage of SP cells accounted for approximately 0.87 ％ of GBC-SD cells. The clone-formed rates of SP was more frequent than that of non-SP cells (14.74％ ± 3.53％ vs 5.17％ ± 1.05％), there was statistically significant difference (t =2.75,P＜0. 05). SP cells could generate tumors with as few as 5 × 103 cells (four of seven animals), whereas at least 1 × 105 non-SP cells were needed to form a tumor (one of seven animals). Re-analysis of SPderived tumors by FACS showed that SP cells under in vivo conditions also have the capacity to regenerate the SP and non-SP fractions. Besides, analysis of Hoechst33342 revealed s small fraction of SP cells, ranging from 0. 27％ to 2.3％ in gallbladder carcinoma specimens. Conclusion SP cells from GBC-SD are highly tumorigenic similar as the cancer stem cells.