Abstract: 【Abstract】ObjectiveTo observe the drug resistance and tumorigenic ability of side population cells （SP cells） which were sorted from BGC-823 cell lines. MethodsSP cells were collected from BGC-823 cells by flow cytometry（FCM）.The cell proliferation of SP cells and nonSP cells were measured by methabenzthiazuron （MTT） assay. The FCM was employed to investigate the inhibitory effect of different concentrations of 5-fluorouracil（5-FU） on BGC-823 cells and measure the proportion and cell cycle of SP cells. The tumorigenic ability of the SP cells was assessed by in vivo transplantation into nonobese diabetic／severe combined immunodeficiency （NOD／SCID） mice. ResultsThere was 0.9％-2.1％ SP cells in BGC-823 cells. It showed that SP cells had a higher proliferative ativity than nonSP cells by MTT assay. The cell numbers of BGC-823 treated by 2.5，5，10，25μg／ml 5-FU for 36h were 2.6×10⁶，2.3×10⁶，2.0×10⁶，1.8×10⁶； and the proportions of SP cells were 12.9％， 9.9％， 4.0％，2.1％, respectively. At the same time， it demonstrated that sorted SP cells has the tougher viability than non-SP cells when suffering with drug treatment. It showed that SP cells were in G0／G1 phase by FCM. The average weights of tumors formed by SP cells（1×10⁴） and non-SP cells（1×10⁴） were 0.577g and 0.150g, respectively. SP cells possessed higher tumorigenicity than nonSP cells， such as tumor growth time and tumor weight. ConclusionSP cells from human gastric cancer cell line BGC-823 possessed a higher proliferative activity and stem celllike drugresistence character. The research of SP cells could provide new targets for antitumor therapy.