Fe3O4 nanoparticles coated with double hydrophilic biocompatible poly(sodium(2-sulfamate-3-carboxylate)isoprene)-b-poly(ethylene oxide) block copolymer were prepared by a one step precipitation method. The magnetic nanoparticles have 15 nm mean diameter (TEM), 68 nm hydrodynamic diameter, -30.10 mV zeta-potential and form very stable dispersion in aqueous media. Structural characterization using powder XRD and Mössbauer spectroscopy establish the magnetite phase, while thermogravimetric analysis and FT-IR spectroscopy confirm the presence of the block copolymer on the nanoparticles surface. The magnetic properties were determined using a vibrating sample magnetometer (VSM) at room temperature and reveal superparamagnetic behavior while the composite materials shows high saturation magnetization up to 67.7 emu/gr.