The aminosilane-modified magnetite nanoparticles were synthesized by the coprecipitation and surface modification with 3-aminopropyltriethoxysilane (APTTS). The superparamagnetic APTTS/Fe3O4 nanospheres with an average diameter of 10nm were characterized significantly with functional group, well dispersion and stabilization in aqueous fluids, as well as a maximized saturation magnetization of 63.54emu/g.