In the enzymatic hydrolysis of biomass, the hydrolysis reaction undergoes a significant decrease in rate and does not reach 100% conversion even after several days of reaction time. One reason may be attributed to enzyme deactivation due to a variety of mechanisms such as thermal, mechanical, and/or chemical activity. Preliminary work was performed here to differentiate between loss of enzyme activity from enzyme-substrate interactions and other interactions of the enzyme in solution that are unrelated to the substrate (termed here as non-specific deactivation). To accomplish this, a series of tests were performed to compare cellulase's activity loss towards freshly added substrate following initial incubation of the enzyme in a buffer-only solution and in a buffer-substrate solution. The results have separated enzyme deactivation into two parts: deactivation due to enzyme-substrate interactions and non-specific deactivation. For high crystalline substrates, the contribution of each is about 50/50. For lower crystalline substrates, the contribution is also about 50/50. Since overall deactivation was less for the lower crystalline substrate, it is inferred that the majority of the deactivation of cellulase comes from exoglucanase.