Effect of temperatures ranging from 20 degrees C to 55 degrees C on fermentative hydrogen production by mixed cultures was investigated in batch tests. The experimental results showed that, at initial pH 7.0, during the fermentative hydrogen production using glucose as substrate, the substrate degradation efficiency and hydrogen production potential increased with increasing temperatures from 20 degrees C to 40 degrees C. The maximal substrate degradation efficiency was 98.1%, the maximal hydrogen production potential was 269.9 mL, the maximal hydrogen yield was 275.1 mL/g glucose and the shortest lag time was 7.0 h. The temperature for fermentative hydrogen production by mixed cultures was optimized to be 40 degrees C. The expanded Ratkowsky models could be used to describe the effect of temperatures on the hydrogen production potential, maximum hydrogen production rate and the lag time during fermentative hydrogen production. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.