Iron oxide nanoparticles were prepared by adding NaBH 4 to aqueous solution of an Fe 3þ salt in the presence of gelatin as the stabilizing reagent. The obtained nanoparticles are relatively unique and can be separated by centrifugation. They can be collected in the dried powder form by centrifugation and freeze-drying. Their structural properties analyzed by transmission electron microscopy, atomic force microscopy and X-ray diffraction, as well as their magnetic properties measured by a superconducting quantum interface device are discussed in this paper.