Fe3O4 magnetic nanoparticles were synthesized by chemical coprecipitation method using ammonia as the precipitator in the present paper. And then cellulase was immobilized on Fe3O4 magnetic nanoparticles via carbodiimide activation, which was testified by FTIR and lots of repeating catalysis experiments. The morphology of nanoparticles immobilized by cellulase was characterized by TEM, and the activity of cellulase was measured by DNS spectrophotometry. The optimum temperature (60 degrees C) and pH value (3.94-5.50) for the catalysis ablility of immobilized cellulose were studied. The result showed that compared with the native enzyme the cellulase immobilized on Fe3O4 magnetic nanoparticles has the advantages of thermal stability, storage stability, and more extensive optimum pH value.