Modification of magnetite nanoparticles via surface-initiated atom transfer radical polymerization (ATRP) was carried out. The magnetic nanoparticles with an initiator group for copper-mediated atom transfer radical polymerization, 3-aminopropyltriethoxysilane chemically bound on their surfaces were prepared by the self-assembled monolayer. Well defined diblock copolymer brushes consisting of poly(ethylene glycol) methacrylate and methyl methacrylate blocks were obtained by using the initial homopolymer brushes as the macroinitiators for the ATRP of the second monomer. The chemical composition of the functionalized magnetite nanoparitcles was characterized by X-ray photoelectron spectroscopy, FT-IR spectroscopy and thermogravimetric analysis. The difference of proteins non-specifically adsorbed onto the surface of uncoated and functionalized magnetite nanoparticles was evaluated. The ability of the functionalized magnetite nanoparticles to resist the proteins non-specific adsorption was higher than that of uncoated nanoparticles.