Cellulase was immobilized on alumina particles for use in fluidized bed type reactors by physical adsorption, cyanogen bromide activation, and cyanogen bromide activation with spacer. Hydrolysis of Avicel was carried out at 50 degrees C and pH 4.5 using these immobilized cellulase (IMC) and the effects of the immobilization method on the reaction performance were investigated. Dependence of the IMC activity on temperature and pH were not altered, as compared with free cellulase. The activity was strongly influenced in the hydrolysis of water-insoluble substrates by the preparation method for immobilizing cellulase. The highest activity was achieved for the IMC prepared by the cyanogen bromide activation with spacer and these values were about ten times greater than the lowest activity for the physical adsorption. Although the activity decreased significantly over the initial reaction period the IMC provided good stability during the reaction, as compared with free cellulase.