Fe3O4/SiO2 nanoparticles with particle size below 30 nm were used as the support for laccase immobilization through glutaraldehyde coupling. Investigation of the immobilized laccase was carried out by X-ray diffractometry (XRD), transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), vibrating sample magnetometry (VSM), UV-vis spectrophotometry, and cyclic voltammogram (CV) measurements. Two phenolic azo dyes, Procion Red MX-5B and azophloxine, were selected to investigate the enzyme activity of the immobilized laccase toward degradation of phenolic azo dyes. The immobilized laccase presents unusual performance for dye decolorization and easy separation with an external magnetic field. Finally, the possible mechanism for the unusual decolorization of phenolic azo dyes by the immobilized laccase is discussed.