Oxidative stress is implicated in atherogenesis; however most clinical trials with dietary antioxidants failed to show marked success in preventing atherosclerotic diseases. We have found that hydrogen (dihydrogen; H 2) acts as an effective antioxidant to reduce oxidative stress [I. Ohsawa, M. Ishikawa, K. Takahashi, M. Watanabe, K. Nishimaki, K. Yamagata, K. Katsura, Y. Katayama, S, Asoh, S. Ohta, Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals, Nat. Med . 13 (2007) 688–694]. Here, we investigated whether drinking H 2-dissolved water at a saturated level (H 2–water) ad libitumprevents arteriosclerosis using an apolipoprotein E knockout mouse (apoE −/− ), a model of the spontaneous development of atherosclerosis. ApoE −/− mice drank H 2–water ad libitum from 2 to 6 month old throughout the whole period. Atherosclerotic lesions were significantly reduced by ad libitum drinking of H 2–water ( p = 0.0069) as judged by Oil- Red-O staining series of sections of aorta. The oxidative stress level of aorta was decreased. Accumulation of macrophages in atherosclerotic lesions was confirmed. Thus, consumption of H 2-dissolved water has the potential to prevent arteriosclerosis.