A quantitative approach was taken to determine the inhibition effects of glucose and other sugar monomers during cellulase and beta-Glucosidase hydrolysis of two types of cellulosic material: Avicel and acetic acid-pretreated softwood. The increased glucose content in the hydrolysate resulted in a dramatic increase in the degrees of inhibition on both beta-Glucosidase and cellulase activities. Supplementation of mannose, xylose, and galactose during cellobiose hydrolysis did not show any inhibitory effects on beta-Glucosidase activity. However, these sugars were shown to have significant inhibitory effects on cellulase activity during cellulose hydrolysis. Our study suggests that high-substrate consistency hydrolysis with supplementation of hemicellulose is likely to be a practical solution to minimizing end-product inhibition effects while producing hydrolysate with high glucose concentration.