Three empirical rate expressions, Kinetics I, II, and III, for the enzymatic hydrolysis of cellulose were evaluated in an effort to develop a easy-to-use rate expression. They are based on the following equation : -dV/dX = kV, where V and X are the hydrolysis rate and the fractional conversion. In Kinetic I, k is constant. In Kinetic II, a linear relatinship between k and t is assumed. In Kinetic III, an exponential relationship is assumed. The three expressions were applied to enzymatic matic hydrolysis carried out under seven different conditions in which the kinds of substrates, enzymes, and initial concentrations were varied. All of the examined rate expressions were applied to the hydrolysis with success, but the better accuracies were obtained by Kinetic III, Kinetic II, and Kinetic I in this order. The variations of k with time found in this study, especially the exponential relationship, were consistent with the effect of the measured changes in the concentration of adsorbed enzyme as predicted by theory developed previously by Ooshima et al. (1).