Here, a simple cellulose conversion model that considers the cellulose surface area and surface density of adsorbed cellulase as substrate-derived and cellulase-derived factors controlling reaction rates is provided. Microcrystalline cellulose (Avicel) and delignifed softwood were used as controls, and structure-modified samples were prepared. It was shown that the initial cellulose conversion rate is largely controlled by the cellulose surface area. Moreover, the proposed model demonstrates that increases in cellulose surface area reduce retardation of the cellulase reaction. The proposed model was used to estimate the impact of structural changes in a substrate (i.e., cellulose surface area) by pre-treatment on enzymatic saccharification. It was found that increasing the cellulose surface area is the most effective way to optimize enzymatic saccharification of cellulose substrates. (C) 2012 Elsevier Ltd. All rights reserved.