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 °C (M) and two organic volumetric loading rates B v : 5 and 8 g sucrose/L.day, with a constant hydraulic residence time of 1 day.The increase of B v 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 v 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 H 2 production in submerged fermentation of moderate concentration of sucrose.