Magnetite Fe3O4 ultrafine powder, a magnetic material, was synthesized by a novel arc-electrodeposition method. The products were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The experimental results showed that the morphologies of the Fe3O4 produced were greatly influenced by the diameters of the metallic iron filament electrodes and the electrolyte composition. (C) 2002 Published by Elsevier Science Ltd.