The effects of initial pH value and Mo-containing additives on biohydrogen production from cassava's stillage were investigated. The biogas composition and individual volatile fatty acids (VFAs) in the liquid phase were determined. The results showed that hydrogen production could be enhanced by adding Mo-containing materials to the mixture of heat-shocked sludge and cassava stillage. The optimum initial pH value ranged from 5.5 to 7.5. The increase of the Mo-containing additive concentration from 1 x 10(-8) mol/L to 1 x 10(-7) mol/L also enhanced biohydrogen production. However, excessive Mo concentrations did not show the same enhancement. Both pH value and Mo-containing additive changed the concentration of final liquid products, but did not change the resultant compounds. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.