A spraying suspension polymerization process for preparation of magnetic polystyrene microspheres with a narrow size distribution was proposed. The magnetite (Fe3O4) nanoparticles with hydrophobic shell were first prepared by a modified chemical coprecipitation method. Then the oil solution, composed of monomer styrene, crosslinker divinylbenzene, Fe3O4 nanoparticles, and initiator benzoyl peroxide, was sprayed into the poly(vinyl alcohol) aqueous solution by a pressure of nitrogen gas to form droplets. Finally, the droplets would be polymerized rapidly to magnetic polystyrene microspheres at the polymerization temperature. The morphology and magnetic properties of microspheres were examined using a scanning electron microscope and a vibrating sample magnetometer. The results showed that the magnetic microspheres had a narrow size distribution with mean diameter of around 10 mu m and smooth surface, and the magnetic microspheres with saturation magnetization of 15.6 emu/g exhibited distinct superparamagnetic characteristics. Powder X-ray diffraction was used to investigate the structure of the magnetite nanoparticles dispersed in the polystyrene matrix. (c) 2005 American Institute of Chemical Engineers.