In the cellulase–cellulose reaction system, the adsorption of cellulase on the solid cellulose substrate was found to be one of the important parameters that govern the enzymatic hydrolysis rate of cellulose. The adsorption of cellulase usually parallels the rate of hydrolysis of cellulose. The affinity for cellulase varies depending on the structural properties of cellulose. Adsorption parameters such as the half-saturation constant, the maximum adsorption constant, and the distribution coefficient for both the cellulase and cellulsoe have been experimentally determined for several substrates. These adsorption parameters vary with the source of cellulose and the pretreatment methods and are correlated with the crystallinity and the specific surface area of cellulose substrates. The changing pattern of adsorption profile of cellulase during the hydrolysis reaction has also been elucidated. For practical utilization of cellulosic materials, the cellulose structural properties and their effects on cellulase adsorption, and the rate of hydrolysis must be taken into consideration.