In this work, Fe3O4/polystyrene/poly(N-isopropylacryl amide-co-methylacrylate acid) (Fe3O4/PS/P(NIPAAM-co-AMA)) magnetic composite latex was synthesized by the method of two stage emulsion polymerization. In this reaction system, 2,2'-azobis(2-methyl propionamidine) dihydrochloride (AIBA) was used as initiator to initiate the first stage reaction and second stage reaction. The Fe3O4 particles were prepared by a traditional coprecipitation method. Fe(3)O4 particles were surface treated by either PAA oligomer or lauric acid to form the stable ferrofluid. The first stage for the synthesis of magnetic composite latex was to synthesize PS in the presence of ferrofluid by soapless emulsion polymerization to form the Fe3O4/PS composite latex particles. Following the first stage of reaction, the second stage of polymerization was carried out by the method of soapless emulsion polymerization with NIPAAM and MAA as monomers and Fe3O4/PS latex as seeds. The magnetic composite particles, Fe3O4/PS/]P(NIPAAM-co-MAA), were thus obtained. The mechanism of the first stage reaction and second stage reaction were investigated. Moreover, the effects of PAA and lauric acid on the reaction kinetics, morphology, and particle size distribution were studied. (C) 2007 Wiley Periodicals, Inc.