Activity of endoglucanase,exoglucanase,cellobiase and filter paper enzyme of four kinds of commercial cellulases were evaluated.Sources of cellulases were mixed,and enzyme activities of these mixtures were then determined.The impact of surfactants on the enzyme activity was studied as well.Results showed that cellobiase was the key factor to the total complex cellulase system.Additionally, the endoglucanases,exoglucanases and cellobiases from different complex cellulase systems were able to act as isoenzymes.The effect of surfactant on the cellulase activity varied with the concentration of the surfactant.Surfactant Tween 80 was added to two of the mixed cellulases in a concentration of 0.01%,which increased the cellulase activity and hastened the degradation of cellulose.