There is increasing interest in the area of enzymatic hydrolysis of biomass to produce bioethanol. Cellulase enzymes play a key role in such applications. Our research has focused on different kinetic aspects of the biodegradation of cellulose substrates, including binding, rate of hydrolysis and inhibitory effects. The aim is to control and optimize the reaction conditions after unveiling the complex adsorption phenomena which occur at the cellulose/cellulase interface. Previous efforts has dealt with the adsorption of cellulase on different cellulosic substrates (different composition, morphology and crystallinity); however, direct inquires on the relationship between cellulase adsorption and substrate surface area have been lacking. Here we report on the adsorption of cellulases on microcrystalline cellulose of different particle sizes under different experimental incubation temperatures. The obtained adsorption isotherms are discussed in terms of relevant enzyme applications and especially in view of our interest to recover and recycle enzymes in bioreactors.