© 2016 Penerbit UTM Press. All rights reserved. The main objective was to separately generate biohydrogen (H 2 ) and biomethane (CH 4 ) with the cassava wastewater via the upflow anaerobic sludge blanket reactors (UASB) under the mesophilic temperature (37 ºC). For the first part, the production of H 2 , the controlled system was managed on the fixed temperature (37 º C) and pH (5.5) included the varied organic concentration in term of chemical oxygen demand (COD) loading rates. As the proper COD loading rate of 25 kg/m 3 d, H 2 and carbon dioxide (CO 2 ) were mainly generated gases which provided the highest specific H 2 production rate of 0.39 l H 2 /l d and the highest H 2 yield of 39.83 l H 2 /kg COD removed. For the second part, the effluent liquid that generated from the stage of H2 production on COD loading rate of 25 kg/m 3 d was fed to the UASB with the fixed temperature (37 °C) and no pH control. The highest specific CH 4 production rate of 0.91 l CH 4 /l d and the highest CH 4 yield of 115.23 l CH 4 /kg COD removed were shown on the proper COD loading rate of 8 kg/m 3 d.