This study examined the sterilization effect of hydrogen water for the under fingernails. First, we selected the standard species that could be infected from the hand. We investigated whether hydrogen water can sterilize the standard species. It was selected to include all of the possible pathogens in the skin such as Gram negative, Gram positive and fungus. The chosen bacteria are Escherichia coli KCTC 1682, Klebsiella pneumoniae ATCC 4352, Pseudomonas aeruginosa KCTC 2004, Shigella sonnei KCTC 2518, Staphylococcus aureus ATCC 6538p and Candida albicans KCTC 7270. All of these strains were sterilized by treatment with hydrogen water. In addition, bacteria were collected from the under fingernails of eight people. The result of 16s rRNA analysis identified that there are ten strains. They are Bacillus megaterium, Brevibacillus borstelensis, Leifsonia shinshuensis, Kurthia gibsonii, Providencia alcalifaciens, Ralstonia pickettii and four types of Staphylococcus spp. These strains under fingernails of six people were sterilized by hydrogen water. When the sporulation bacteria B. borstelensis and K. gibsonii coexisted, Ralstonia pickettii was sterilized 81%. In all other cases, more than 93% was sterilized. The sterilizing power of hydrogen water differed depending on the type of bacteria, but hydrogen water sterilized a considerable part of pathogenic bacteria under the nails. In conclusion, washing hands using hydrogen water could greatly improve the hygiene of customers in the nail shop where the hygiene control of hands and nails is important.