This article reports a novel type of composite microspheres showing magnetic properties. The composite microspheres consist of Fe3O4, silica, and poly(gamma-benzyl-L-glutamate) (PBLG). For preparing such composite microspheres, Fe3O4 nanoparticles were fabricated by the solvothermal method and then coated with a silica shell by tetraethoxysilane. Subsequently, amino groups were introduced on the above Fe3O4-silica spheres by using 3-aminopropyltriethoxysilane. Finally, the obtained spheres were used as initiator for polymerizing gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA), providing the anticipated magnetic composite microspheres. Such microspheres were characterized by FT-IR, TEM, large-angle powder XRD, and vibrating sample magnetometer. FT-IR spectra demonstrated that the PBLG chains adopted alpha-helical conformations. The magnetic composite microspheres showed a high saturation magnetization of 34.1 emu/g and the expected rapid magnetic responsivity. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.