Our goal is to develop, characterize and optimize functionalized super paramagnetic iron oxide nanoparticles (SPION) demonstrating the capacity to be internalized by human cancer cells. SPION (mean diameter 9nm) were coated with various ratios to iron oxide of either polyvinyl alcohol (PVA), carboxylate-functionalized PVA, thiol-functionalized PVA and amino-functionalized PVA (amino-PVA). The interaction with cells and cytotoxicity of the SPION preparations were determined using human melanoma cells. From the four functionalized SPION preparations, only the amino-PVA SPION demonstrated the capacity to interact with, and were not cytotoxic to, human melanoma cells. This interaction with melanoma cells was dependent on the amino-PVA to iron oxide ratio, was an active and saturable mechanism displayed by all cells in a culture. These functionalized SPION were characterized by transmission electron microscopy and electrophoretic mobility. The physical comportment of SPION changed at specific PVAs to iron oxide ratios, and this ratio corresponded to the ratio of optimal interaction with cells. In conclusion, the successful development of functionalized SPION displaying potential cellular uptake by human cancer cells depends both on the presence of amino groups on the coating shell of the nanoparticles and of its ratio to the amount of iron oxide