Algal biomass is a promising raw material for production of third-generation biohydrogen. Few studies have investigated how the concentration of galactose, the main monosaccharide of algae biomass, affects fermentative production of H-2. We isolated a new culture of H-2-producing bacterium from an anaerobic sludge. This culture was identified as Clostridium beijerinckii based on the sequence of the 16S rRNA gene and was named C. beijerinckii Br21 (KT626859). The isolated culture produced the highest amount of H-2 at 35 degrees C and initial pH 7. The isolate used many carbon sources to produce H-2, including the monosaccharides glucose, galactose, and mannose resulting from algae biomass hydrolysis. For the first time, fermentation batch tests based on galactose as carbon source showed that production of H-2 by a C. beijerinckii strain depended on the concentration of galactose. Galactose at 15 g/L provided the highest rate and yield of H-2 production, 117.45 mL of H-2/L.h and 2.02 mol of H-2/mole of galactose, respectively; the main metabolites from galactose fermentation were butyric acid (61%) and acetic acid (24%). Therefore, C. beijerinckii Br21 is a promising candidate for fermentative production of H-2 from galactose and algae biomass. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.