Magnetite-polyoxometalate hybrid nanomaterials were prepared by surface modification of magnetite nanoparticles with polyoxometalates. Silica coating of magnetite nanoparticles with tetraethyl orthosilicate and then functionalization with aminopropyl trimethoxy silane (APTS) yielded aminopropyl modified silica coated magnetite nanoparticles (APTSCMNPs). Reaction of the resulted nanoparticles with H3PMo12O40 and H3PW12O40 heteropoly acids produced hybrid nanomaterials, PMo-APTSCMNPs and PW-APTSCMNPs, respectively. The resulted nanomaterials were characterized with different physicochemical techniques such as Fourier transform infrared (FT-IR) and atomic absorption spectroscopies. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and thermogravimetric analyzes (TGA and DTA). VSM analysis showed superparamagnetic properties of the materials and TEM and SEM analyses indicated the relatively uniform spherical nanoparticles with 20 nm average size. (C) 2011 Elsevier B.V. All rights reserved.