The effects of woody biomass mixtures were investigated on the rates of hemicellulose hydrolysis by dilute acid. Very good agreement between the model predictions and single species acid hydrolysis data confirmed the validity of a pseudo first-order model approach. This model was then utilized to predict monomer sugar concentrations for mixtures of hardwood (aspen, basswood, and red maple), a softwood (balsam), and the energy crop switchgrass, with very good agreement. The results of this study show that there are not significant synergistic or antagonistic effects by mixtures of woody biomass species on the kinetics of hemicellulose hydrolysis by dilute acid. Kinetic parameters were developed for each woody biomass species with xylose formation activation energies ranging from 76.19-171.20 kJ/mol, and pre-exponential factors ranging from 2.19 x 10(8)-7.73 x 10(19) min(-1). Overall xylose yields for pure biomass species ranged from approximately 66-88% with balsam having the lowest yield and switchgrass producing the highest yield. (C) 2008 American Institute of Chemical Engineers.