Dioscorea batatas Decne (DBD) is traditionally used to heal inflammatory disease as a folk medicine. It was reported that a glycoprotein (DBD glycoprotein) with a molecular weight of 30 kDa was isolated from DBD and consists of carbohydrate (83.75%) and protein (16.25%) moieties. The previous results showed that it has a strong scavenging activity against hydroxyl radicals without any pro-oxidant activity in the cell-free system. The purpose of the present study was to show whether or not the DBD glycoprotein inhibits cell proliferation-related signal transduction stimulated by bisphenol A (BPA, an environmental hormone) in Chang liver cells. The results in this study indicated that DBD glycoprotein (200 microg ml(-1)) has suppressive effects on abnormal cell viability, production of intracellular reactive oxygen species (ROS) and nitric oxide (NO) in BPA (50 microM)-induced Chang liver cells by blocking the phosphorylation of mitogen-activated protein kinase (MAPK) and activating protein-1 (AP-1) activity. In addition, DBD glycoprotein (200 microg ml(-1)) normalized the activity of catalase (CAT) and glutathione peroxidase (GPx). Consequently, DBD glycoprotein inhibits the expression of proliferating cell nuclear antigen (PCNA, cell proliferation maker) stimulated by BPA. Therefore, it is speculated that DBD glycoprotein protects against carcinogenic events caused by BPA in Chang liver cells.