Pickering suspension polymerization was used to prepare magnetic polymer microspheres that have polymer cores enveloped by shells of magnetic nanoparticles. Styrene was emulsified in an aqueous dispersion of Fe(3)O(4) nanoparticles using a high shear. The resultant Pickering oil-in-water (o/w) emulsion stabilized solely by magnetic nanoparticles was easily polymerized at 70 degrees C without stirring. Fe(3)O(4) nanoparticles act as effective stabilizers during polymerization and as building blocks for creating the organic-inorganic hybrid nanocomposite after polymerization. The fabricated magnetic nanocomposites were characterized by FTIR, XRD, TGA, DSC, GPC, XPS and SEM. The structures of the polymer core and the nanoparticle shell were analyzed. We investigated the effects on the products of the weight of Fe(3)O(4) nanoparticles used to stabilize the original Pickering emulsions. Pickering suspension polymerization provides a new route for the synthesis of a variety of hybrid nanocomposite microspheres with supracolloidal structures. (C) 2009 Elsevier Ltd. All rights reserved