Today we find several varieties of hydrogen water in stores. This suggests that there has been a growing interest in this product among people who are concerned about their health and beauty. Hydrogen can be effective in reducing excess active oxygen in the body, and hydrogen water contains molecular hydrogen. Therefore the author measured antioxidative activities of 5 kinds of commercial hydrogen water and for comparison 2 kinds of alkaline ionized water using the Biological Anti-oxidant Potential（BAP）testing method. Commercial hydrogen waters were found to have antioxidative activities of about 200 to 450μmol/L. One of the alkaline ionized waters showed antioxidative activity of about 430μmol/L.