Novel magnetic polymer microspheres with amphiphilic structure ranging in diameter from 5 to 80 mum were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) acrylamide macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing initiator concentration. It also increased with decreasing stabilizer concentration and MPEO concentration. The content of the amino groups localized in the microspheres ranged from 0.01 to 0.25 mmol/g. (C) 2003 Wiley Periodicals, Inc.