A versatile route applied to the synthesis of thermoresponsive magnetite nanoparticles involved the formation of nanoparticles by coprecipitation of Fe2+/Fe3+ in the presence of an alkaline solution, followed by attachment of the reversible addition-fragmentation transfer (RAFT) agents onto the surface of the Fe3O4 nanoparticles via the electrostatic interactions, subsequent grafting from polymerization of N-isopropylacrylamide (NIPAM) through surface-initiated RAFT polymerization. The surface-initiated RAFT polymerization can be conducted in a well-controlled manner, as revealed by the linear kinetic plot, linear evolution of number-average molecular weights (M (n) ) versus monomer conversions, and the relatively narrow molecular weight distributions (M (w) /M (n) < 1.5) of the grafted PNIPAM chains. The as-synthesized hybrid nanoparticles showed thermoresponsive behavior and were characterized by FTIR, XPS, TGA, VSM, DLS, and TEM, etc.