Fe3O4/P(St NIPAM) thermosensitive magnetic microspheres with core/shell structure were prepared by copolymerization of styrene(St) and N isopropylacrylamide(NIPAM) in the presence of Fe3O4 magnetic fluid in ethanol/water medium. The content of Fe3O4 is about 20～100mg/g in the microspheres. The hydrodynamic diameter of Fe3O4/ P(St NIPAM) is depended on temperature and shrank above the lower critical solution temperature (LCST) in water. Thermosensitive magnetic microspheres with average diameter size range from 5 to 100μm were obtained by different reaction conditions.Higher initiator concentration formed larger Fe3O4/P(St-NIPAM) microshpheres

Ethanol played important roles in the polymerization

while the stabilizer PEG has smaller effrct for the size of Fe3O4/P(St-NIPAM) microspheres.