Extremely halotolerant hydrogen-producing bacteria were investigated, owing to their ability to live in high-salinity conditions. Based on this characteristic, it was hypothesized that extremely halotolerant hydrogen-producing bacteria can tolerate high concentrations of Na+ ions. To test this hypothesis, we investigated the characteristics of extremely halotolerant hydrogen-producing bacteria obtained from salt-damaged soil in Khon Kaen and a commercial salt pan field near Bangkok (Samut Sakhon), Thailand. The result of this preliminary investigation showed that hydrogen production under saturated conditions of 26% (6 M) NaCl was possible after one year of acclimatization. The extremely halotolerant hydrogen-producing bacteria in this study were also confirmed to have a requirement for Cl- ions for hydrogen production. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.