Antitumor activities of onion methanol extract (OME) and onion Kimchi methanol extract (OKME) were investigated by using aflatoxin -mediated Salmonella typhimurium mutagenicity and the model of cytotoxicity on the cancer cell lines. Their immune activities were also investigated by using mouse spleen cells and macrophage cell lines, respectively. OME and OKME showed the enhanced antimutagenicity in a dose-dependent manner in particular, the activity of OKME was higher than that of OME. OME and OKME decreased over 20% of the proliferation of the A549 (lung cancer cell) and MCF-7 (breast cancer cell) cell lines when compared with the control at 1,000 g/mL. The proliferation of mouse spleen cells and the NO production in marcrophage cell lines treated OME and OKME were increased in a dose-dependent manner compared with untreated control cells, and their activities of OKME were higher than those of OME.