Glyceollins are synthesized from daidzen in soybean elicited with Aspergillus sojae. Several studies reported that glyceollins had anti-estrogenic, anti-inflammatory, and anticancer activities in both breast cancer cell and animal models. This study was aimed at investigating whether glyceollins exert anticancer activity through regulation of phase 2 detoxifying enzymes. That is, I was interested in investigating if glyceollins can inhibit DMBA-induced breast cancer development by enhancing xenobiotic metabolizing enzymes such as glutation S -transferase, glucuronyl transferase, and sulfotransferase. The expression of phase 2 enzymes in organs collected from mice was assessed by Western blot, immunohistochemistry(IHC). Also we observed the tumor formation in mammary gland mice by whole mount analysis. The number of fat pad TEBs in the mammary tissue was significantly increased by DMBA treated and reduced by treatment with glyceollins. Also glyceollins were found to induce same antioxidant/detoxifying enzymes in the tissue. Therefore, we suspected that DMBA had little effect on mammary tissue as it was rapidly metabolized by detoxifying enzymes induced by glyceollins. In conclusion, glyceollins appear to protect effect to tissue from chemical carcinogen.