The main objective was to separately generate biohydrogen (H2) and biomethane (CH4) 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 H2, 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/m3 d, H2 and carbon dioxide (CO2) were mainly generated gases which provided the highest specific H2 production rate of 0.39 l H2/l d and the highest H2 yield of 39.83 l H2/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/m3 d was fed to the UASB with the fixed temperature (37 °C) and no pH control. The highest specific CH4 production rate of 0.91 l CH4/l d and the highest CH4 yield of 115.23 l CH4/kg COD removed were shown on the proper COD loading rate of 8 kg/m3 d.