Despite the intense progress achieved in processing the magnetic particle imaging (MPI) technology, there is no suitable tracer that satisfies all MPI requirements. For this purpose, dextran-coated superparamagnetic iron oxide nanoparticles (SPIONs) were designed and synthesized as appropriate MPI tracer. To ensure a prospective biosafe application of these nanoparticles, we started to evaluate the biocompatibility, including cell toxicity and cellular uptake. The SPIONs internalized into mouse fibroblast cells were showing good labeling efficiencies and a cytosolic accumulation. Flow cytometry analysis demonstrated no difference of the cell viability of labeled cells in comparison with unlabeled control cells. But we observed decreased cell proliferation in response to increased SPION concentrations. In conclusion, SPIONs could reveal harmful properties and, therefore, further experiments should be considered.