The aim of this work was to compare the H-2 production in a lab scale anaerobic fluidized bed bioreactors (AFBRs) at two levels of operational temperature: ambient temperature (A) and 35 degrees C (M) and two organic volumetric loading rates B-nu: 5 and 8 g sucrose/L.day, with a constant hydraulic residence time of 1 day. The increase of B-nu from 5 to 8 g sucrose/L. day had a positive effect on the performance of our anaerobic fluidized bed reactors. In conclusion, at a B-nu of 8 g sucrose/L.day the average performance of AFBR-A was superior to that of AFBR-M: 1.8 times for the H-2 concentration in the biogas (54% and 31% respectively) and 2.2 times for the H-2 productivity (920 and 427 NmLH(2)/L-bed day, respectively). The H-2 production in an AFBR operated at ambient temperature was superior to that of the mesophilic units and showed encouraging results for H2 production in submerged fermentation of moderate concentration of sucrose. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.