Fe3O4／P(NaUA-St-BA) core-shell magnetic composite nanoparticles were prepared by soapless polymerization of styrene and butyl acrylate in the presence of Fe3O4 magnetic colloidal particles coated with a reactive suffaetant NaUA and their diameter was about 10nm．The results of IR and TG analysis demonstrated that the desired polymer was bonded to the surface of Fe3O4 partieles．The morphology analysis by TEM confirmed that the composite particles had a core-shell structure and a relatively uniform diameter of about 60nm．The results of TG analysis indicated that the coating amount of NaUA and P(NaUA-St-BA) copolymer on Fe3O4 particles was 13.83％ and 71.85％．respectively The magnetic properties of the obtained composite particles were measured by VSM．and superparamagnetic properties was found Finally

the prepared magnetic composite particles latexes were stable for several months.