The effect of several inhibitors on the reaction rate in the enzymatic hydrolysis of cellulolytic substrate （solka floc BW 200） was studied. The enzyme used was produced from Trichoderma reesei QM 9414, and the inhibitors used were cellobiose, glucose, ethanol, xylose and sucrose, respectively. In general, the decreasing effect for the reducing sugar production was observed as the amount of the inhibitors were increased, and the increasing effect of the soluble protein was also observed, except ethanol. The measurements of both the filter paper activity and CMC activity were carried out for the case of glucose and ethanol, respectively. The activities were decreased to about 66 % and about 70 % from the initial activities. Analysis of the data using Foster-Niemann plot indicated that the inhibition was of the competitive type. The inhibition constant values of each inhibitor were calculated form the plot.