A thermophilic hydrogen producer was isolated from hot spring sediment and identified as Thermoanaerobacterium thermosaccharolyticum KKU19 by biochemical tests and 16S rRNA gene sequence analysis. The strain KKU19 showed the ability to utilize various kinds of carbon sources. Xylose was the preferred carbon source while peptone was the preferred organic nitrogen source. The optimum conditions for hydrogen production and cell growth on xylose were an initial pH of 6.50, temperature of 60 degrees C, a carbon to nitrogen ratio of 20:1, and a xylose concentration of 10.00 g/L. This resulted in a maximum cumulative hydrogen production, hydrogen production rate and hydrogen yield of 3020 +/- 210 mL H-2/L, 3.95 +/- 0.20 mmol H-2/L h and 2.09 +/- 0.02 mol H-2/mol xylose consumed, respectively. Acetic and butyric acids were the main soluble metabolite products suggesting acetate and butyrate type fermentation. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.