Marine algae are promising alternative sources for bioenergy including hydrogen. Their polymeric structure, however, requires a pretreatment such as dilute-acid hydrolysis prior to fermentation. This study aimed to optimize the control variables of batch dilute-acid hydrolysis for dark hydrogen fermentation of algal biomass. The powder of Gelidium amansii was hydrolyzed at temperatures of 120-180 degrees C, solid/liquid (S/L) ratios of 5-15% (w/v), and H2SO4 concentrations of 0.5-1.5% (w/w), and then fed to batch hydrogen fermentation. Among the three control variables, hydrolysis temperature was the most significant for hydrogen production as well as for hydrolysis efficiency. The maximum hydrogen production performance of 0.51 L H-2/L/hr and 37.0 mL H-2/g dry biomass was found at 161 164 degrees C hydrolysis temperature, 12.7-14.1% S/L ratio, and 0.50% H2SO4. The optimized dilute-acid hydrolysis would enhance the feasibility of the red algal biomass as a suitable substrate for hydrogen fermentation. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.