The objective of this study was to produce hydrogen and methane from cassava wastewater using two steps of upflow anaerobic sludge blanket reactors (UASB), emphasizing maximum hydrogen production. For the first hydrogen production stage, the UASB system was operated at 37 degrees C and pH 5.5 at different COD loading rates. A maximum specific H-2 production rate of 0.391 H-2/l d and a maximum H-2 yield of 39.831 H-2/kg COD removed were found at a COD loading rate of 25 kg/m(3)d and the gas produced contained 36.4% H2, and 63.6% CO2 without methane. For the second methane production stage, the UASB was fed by the effluent produced from the hydrogen production step operated at the optimum COD loading rate. A maximum specific CH4 production rate of 0.911 CH4/l d and a maximum CH4 yield of 115.23 1 CH4/kg COD removed were found at a COD loading rate of 8 kg/m(3)d. The inhibition levels of organic acids to acidogens and methanogens were found to be 10,000 and 400 mg/l as acetic acid, respectively. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.