This manuscript presents a review about the state of the art in the electrochemical synthesis of nanosized magnetic metal oxides. Anodic oxidation of metal salts in solution or sacrificial metal electrodes allows the preparation of nanometric magnetic materials, in particular iron oxides. Synthetic conditions, such as the nature of the electrolyte, its concentration, pH, current density, or potential, play an important role on the material’s nature, purity and particle size and distribution will be discussed. Special attention is drawn to the mechanism of particle formation. Colloidal properties of magnetic oxides in terms of water stability as a function of pH and particle surface charge are considered. The magnetic properties as a function of the particle size and crystallinity are also taken in account in this work for pure magnetic iron oxide nanoparticles synthesized by electrooxidation.