Although various antioxidants have been tested as therapeutics for endotoxemic subjects, the results of their efficacy are conflicting. Antioxidant biofactor (AOB) is a unique processed grain food that exhibits strong antioxidant activity (Minamiyama et al, J Nutr Sci Vitaminol, 40: 467-477, 1994). The present study was carried out to test the effect of AOB on hepatic injury in rats induced by lipopolysaccharide (LPS). Intravenous administration of LPS induced liver injury with a concomitant increase in hepatic generation of nitric oxide (NO) and 4-hydroxy-2-nonenal (HNE) modified proteins in the control group. The administration of AOB significantly inhibited the LPS-induced hepatic injury and generation of HNE-modified proteins and increased the survival rate of endotoxemic rats without affecting NO generation and plasma levels of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). AOB scavenged superoxide radicals without affecting NO production by LPS-stimulated macrophage cell line J 774.2 cells. AOB also inhibited lipid peroxidation induced by LPS in the cells. These results suggested that AOB might scavenge superoxide radicals and decrease toxic metabolites including HNE, thereby inhibiting liver injury in endotoxemic rats.