PROBLEM TO BE SOLVED: To provide a method for inexpensively and easily producing ionized hydrogen water containing Hions using microorganisms, and the microorganism for decomposing hydrogen to generate Hions.SOLUTION: A method for producing ionized hydrogen water includes a step of bringing water and microorganisms into contact to produce ionized hydrogen water containing H(hydride) ions. The microorganisms belong to one of Bradyrhizobium genus, Mesorhizobium genus, Burkholderia genus and Novosphingobium genus, and the microorganisms belong to one of Bradyrhizobium G+O-O strain, Mesorhizobium GNI strain indicated by Accession No. NITE ASP-1240, Burkholderia sp. WN1 strain indicated by Accession No. NITE AP-1241, and Novosphingobium G+O-G strain indicated by Accession No. NITE AP-1251.