Histidine-rich glycoprotein (HRG) has been reported to have regulatory effects on blood coagulation and fibrinolytic systems. In addition to these effects, we found that HRG is a factor that is specifically downregulated in sepsis, and that HRG contributes to the amelioration of sepsis via its effects on maintaining neutrophil morphology and function and protecting vascular endothelial cells. The involvement of ROS in the progression of septicemia has been reported, and in previous report, we have shown that HRG suppresses excess ROS production from neutrophils, but the direct effects of HRG on ROS and ROS-producing systems are not known. Therefore, in this study, we investigated the activity of HRG against ROS. HRG showed no effect on superoxide and oxygen peroxide among ROS, but on hydroxyl radicals, which are highly toxic in vivo, it was found that HRG suppressed the production of hydroxyl radicals by efficiently chelating the divalent iron ions used in the Fenton reaction during the production of hydroxyl radicals. With regard to peroxyl radicals involved in lipid peroxidation, which is important for cell damage, HRG exhibited antioxidant capacity even though it was not mediated by the Fenton reaction, suggesting that in this system, the antioxidant capacity was due to autoxidation.