We report the preparation and magnetic properties of magnetite Fe3O4 nanostructures grown by electrodeposition in the form of (i) nanocrystalline film (200 nm thick) and ( ii) nanocylinders (50 nm diam, 200 nm long! inside the pores of polycarbonate membranes. According to x-ray diffraction and magnetic measurements, the electrodeposited materials have a good quality but may exhibit strain and possible small departure from the precise Fe3O4 stoichiometry. The magnetic properties of these materials are discussed in term of shape magnetic anisotropy, antiphase boundary interactions and the Verwey transition. (C) 2005 The Electrochemical Society.