The synthesis of magnetic coreshell nanoparticles consisting of magnetite cores surface-functionalized by glycolic acid covered by polylactic acid was performed by applying the grafting-from strategy, where the polymerization is initiated from the particle surface. The surface initiated ring-opening polymerization of D,L-lactide was initiated by tin (II) 2-ethylhexanoate using microwave irradiation. Coreshell nanoparticles of high colloidal stability in water were obtained in this way. The morphology of the magnetic coreshell nanostructure was determined by transmission electron microscopy, and the chemical structure was elucidated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy. Magnetic measurements revealed superparamagnetic behavior and high magnetization values. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012