Magnetic poly(methyl methacrylate) (PMMA) microspheres were prepared by double-miniemulsion polymerization. First, oleic acid coated magnetite particles synthesized by means of coprecipitation were dispersed into octane to obtain a ferrofluid. The ferrofluid and MMA were emulsified to form O/W emulsion, respectively. Subsequently two miniemulsions were mixed together for polymerization. The obtained magnetic polymer particles were characterized by, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and thermogravimetry. The results showed that oleic acid coated magnetite particles were well encapsulated in PMMA. The effects of initiator dosage and monomer concentration on the conversion of MMA were also investigated. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 112:89-98, 2009