boswellia sacra flueck essential oil is obtained from frankincense obtained from boswellia sacra trees. the aim of this study was to investigate the in vitro anti-cancer activity of boswellia sacra (bs) essential oil in cd133+ and cd133- colo-320 cells. essential oil was analyzed by gc-ms. cd133+ cells, cancer stem cells, were obtained from the colo-320 by the minimacs system. cytotoxicity were evaluated with mtt assay. anti-cancer activity of bs essential oil was investigated by immunocytochemistry. 41 compounds were identified in the essential oil. 1:2 dilution bs essential oil was found to be active against all the cells for 24 h incubation. -catenin immunoreactivity was significantly decreased in both bs essential oil-treated cd133+ and cd133- colo-320 cells. caspase-3 immunoreactivity significantly increased in bs essential oil-treated cd133- colo-320 cells. we conclude that bs essential oil decreased -catenin signaling molecules which play a crucial role in cancer cell proliferation. bs essential oil promoted apoptosis in cd133- colo-320 cells.