Iron oxide nanoparticles obtained by the coprecipitation of Fe(II) and Fe(III) salts and oxidation were coated with a novel poly(vinyl acetate-co-5-tert-(butylperoxy)-5-methylhex-1-en-3-yne-co-butyl acrylate-co-maleic anhydride) (PVBM) oligomer to ensure colloidal stability. The magnetic nanoparticles were thoroughly characterized by a range of physico-chemical methods, which proved the presence of the coating on the particles. Experiments with rat mesenchymal stem cells (rMSCs) confirmed that PVBM-coated gamma-Fe2O3 nanoparticles were not cytotoxic and that the average efficiency of stem cell labeling was good and comparable to that obtained with commercial agents. The cells labeled with PVBM-coated gamma-Fe2O3 nanoparticles displayed excellent contrast on magnetic resonance (MR) images. Such particles are thus promising for in vivo MR imaging of transplanted cells. Moreover, PVBM offers the possibility of additional modification by grafting compounds that reduce non-specific protein adsorption.