The aim of the work here described is the synthesis of magnetic nanoparticles (MNPs) for the inclusion into human Red Blood Cells (RBCs) and as potential contrast agent for magnetic resonance imaging (MRI). Synthesis, characterization and preliminary in vitro tests are the main topics. Superparamagnetic iron oxide nanoparticles and manganese/zinc ferrite nanoparticles have been synthesized, by using wet-chemistry techniques such as co-precipitation and thermal decomposition methods. For biomedical application, a suitable surface coating must be grafted to MNPs surface, to preserve the colloidal stability even in physiological condition. Therefore, a biomimetic coating based on non-modified dextran was grafted to MNPs for ensuring optimal stability and low toxicity for the inclusion in living RBCs.