In this study, the poly(NIPAAm-MAA)/Fe3O4 hollow latex particles were synthesized by three steps. The first step was to synthesize the poly(methyl methacrylate-co-methylacrylate acid) (poly(MMA-MAA)) copolymer latex particles by the method of soapless emulsion polymerization. Following the first step, the second step was to polymerize N-isopropylacrylamide (NIPAAm), MAA, and crosslinking agent (N,N'-methylene-bisacrylamide (MBA)) in the presence of poly(MMA-MAA) latex particles to form the linear poly(MMA-MAA)/crosslinking poly (NIPAAm-MAA) core-shell latex particles. After the previous processes, the core-shell latex particles were heated in the presence of NH4OH to dissolve the linear poly(MMA-MAA) core in order to form the poly(NIPAAm-MAA) hollow latex particles. In the third step, Fe2+ and Fe3+ ions were introduced to bond with the -COOH groups of MAA segments in the poly(-NIPAAm-MAA) hollow polymer latex particles. Further by a reaction with NH4OH and then Fe3O4 nanoparticles were generated in situ and the poly(NIPAAm-MAA)/Fe3O4 magnetic composite hollow latex particles were formed. The concentrations of MAA, crosslinking agent (N,N'-methylene bisacrylamide), and Fe3O4 nanoparticles were important factors to influence the morphology of hollow latex particles and lower critical solution temperature of poly(NIPAAm-MAA)/Fe3O4 magnetic composite hollow latex particles. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 2626-2634, 2012