“Grafting from” surface-initiated nitroxide-mediated radical polymerization (SI-NMRP) techniques were used to synthesize poly[styrene-co-(maleic anhydride)] copolymer brushes from the Fe3O4 surfaces. Well-defined polymer chains were grown from the Fe3O4 surfaces to yield particles with a Fe3O4 core and a polymer outer layer. The observed narrow molecular weight distributions (Mw/Mn), linear kinetic plots and linear plots of molecular weight (Mn) versus conversion for the free polymer indicated that the chain growth from the Fe3O4 surface was a controlled process by adding an excess of 2,2,6,6-tetramethylpiperidinyloxy (TEMPO). The modified nanoparticles were subjected to detailed characterization using XRD, TEM, FT-IR, and TGA. The analyses of vibration sample magnetometer (VSM) verified that the nanoparticles owned good magnetic property. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers