Magnetic (Fe3O4) nano particles are very promising materials for many biomedical applications because of their ability to be manipulated and detected with an external magnetic field. In the present investigation a systematic approach has been proposed to prepare temperature-sensitive magnetic nano composite polymer particles. Nano-sized Fe3O4 particles were first prepared by co-precipitation of Fe2+(aq) and Fe3+(aq) in presence of aqueous NaOH solution. Fe3O4 nano particles were then functionalized with a silane coupling agent followed by two step polymerization. In the first step radical copolymerization of styrene and N-isopropyl acrylamide (NIPAM) was carried out in presence of functionalized Fe3O4 as seed particles. The produced latex particles were named as Fe3O4/P(S-NIPAM). Then seeded copolymerization of NIPAM, methacrylic acid (MAA) and N,NÂ-methylene-bis-acrylamide (MBAAm) was carried out in presence of Fe3O4/P(S-NIPAM) composite seed particles. The final composite polymer particles named as Fe3O4/P(S-NIPAM)/P(NIPAM-MAA-MBAAm) were characterized by electron micrographs, FTIR, and thermogravimetric analyses. The magnetic nano composite polymer particles containing carboxyl groups exhibited temperature-sensitive phase transition at temperature close to 30°C.