Abstract: Rosin was reacted with 2-hydroxyethyl methacrylate and an ester (denoted as RH) was formed. Then polymerization was carried out in the presence of oleic acid-modified Fe3O4 magnetic fluid, with RH and styrene (St) as monomers, divinylbenzene (DVB) as cross-linking monomer, gelatin as dispersant, 2,2-azobisiso-butyronitrile (AIBN) as initiator. The magnetic polymer microspheres with rosin moiety were prepared by suspension polymerization and the effect of the magnetic fluid content on the magnetic polymer microspheres was investigated. The structures and properties of the magnetic polymer microspheres were characterized by Fourier transform-infrared spectroscopy, thermogravimetry, X-ray powder diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectrometer. Hysteresis loops of the microspheres were tested by magnetic measuring system. The results indicated that at a monomer ratio of m(RH):m(St):m(DVB)=1:1.5:0.4, and the amounts of AIBN and gelatin about 1% and 6% of the total monomers, respectively, the products were spherical with high superparamagnetism. When the amount of oleic acid-modified Fe3O4 increased, the particle sizes of microspheres were gradually increased, the particle size distribution was broadened, and the saturation magnetic intensity increased.