The effect of temperature on the hydrogen fermentation of cellulose was evaluated by a continuous experiment using a mixed culture without pretreatment. The experiments were conducted at three different temperatures, which were mesophilic [37 +/- 2 degrees C], thermophilic [55 +/- 2 degrees C] and hyper-thermophilic [80 +/- 2 degrees C), with an influent concentration of cellulose of 5 g/l and a hydraulic retention time [HRT] of 10 days. A stable hydrogen production was observed at each condition. At 37 +/- 2 degrees C the maximum hydrogen yield was 0.6 mmol H-2/g cellulose. However, at 55 +/- 2 degrees C and 80 +/- 2 degrees C, the maximum hydrogen yields were 15.2 and 19.02 mmol H-2/g cellulose, respectively. While 26% of the biogas was methane under the mesophilic temperature, no methane gas was detected under both the thermophilic and hyper-thermophilic temperatures. The results show that operational temperature is a key to sustainable bio-hydrogen production and that the thermophilic and hyper-thermophilic conditions produced better results than mesophilic condition. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.