Hydrogen production from sucrose in a granule-based upflow anaerobic sludge blanket (UASB) reactor was optimized through employing response surface methodology (RSM) with a central composite design in this study. The individual and interactive effects of influent sucrose concentration (S-in) and hydraulic retention time (HRT) on anaerobic hydrogen production were elucidated. Experimental results show that a maximum hydrogen yield of 1.62mol-H-2/mol-hexose was obtained under the optimum conditions Of Sin 14.5 g/L and an HRT 16.4 h. The hydrogen yield was individually dependent on S-in and HRT, while their interactive effect on the hydrogen yield was not significant. Throughout the experiments the hydrogen content fluctuated between 25.9% and 50.0%, but free of methane. Ethanol, acetate and butyrate were the main aqueous products and their yields all correlated well with S-in and HRT, indicating a mixed-type fermentation in this UASB reactor. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.