Magnetic nanoparticles have a large variety of applications in biomedicine such as hyperthermic treatment of tumors, magnetically targeted drug delivery by magnetic carriers. In this work , our purpose is the preparation of biocompatible polymer modified magnetite nanoparticles for magnetite resonance imaging(MRI). We synthesized of magnetic nanoparticles treated with silane-functional molecules which allow the expression of amine end groups on the nanoparticles surface. Afterwards, these functional end groups are used to graft biocompatible materials such as poly(ethylene glycol). We studied the in vitro toxicity of the polymer modified magnetite nanoparticles in the 293T cell line.