A simple preparation process was developed for magnetic nanoparticles, consisting of chitosan coated on Fe3O4 nanoparticles, to be used as support for enzyme immobilization. Cellulase was covalently immobilized on this magnetic support using glutaraldehyde as a coupling agent. The structure, morphology, and magnetic property of the support were studied by X-ray diffraction, vibrating-sample magnetometer, thermogravimetric analysis, transmission electron microscopy, and Fourier transform infrared (FT-IR) spectroscopy. The properties of the immobilized cellulase were investigated by regarding activity, optimum operational pH and temperature, thermal stability, and reusability. The amount of cellulase on the nanoparticles reached 112.3 mg/g. The characterization and determination results showed that the immobilized cellulase had higher operational stability than the free enzyme over wider temperature and pH ranges and good reusability after recovery by magnetic separation. Therefore, these magnetic Fe3O4-chitosan nanoparticles are expected to be a useful support for enzyme.