Poly(ethylene oxide) macromonomer (MPEO) was synthesized by the reaction of acryloyl chloride and biamino poly (ethylene oxide) (NH2-PEO-NH2) prepared from PEG by Gabriel reduction. Amphiphilic polymer magnetic microspheres containing amino groups were prepared by dispersion copolymerization of styrene and MPEO in the presence of Fe3O4 magnetic fluid in ethanol/water medium．The content of the amino groups localized in the microspheres ranged from 0.01 to 0.25 mmol/g．The amphiphilie magnetic miemspheres ranging in diameter from 5 to 80μm could be prepared by changing dispersion polymerization conditions．The mechanism of magnetic miemspheres nucleation and growth was discussed．