A novel method to prepare iron oxide nanoparticles by precipitation in bicontinuous microemulsions is reported. Precipitation reactions were carried out in microemulsions stabilized with a mixture of dodecyltrimethylammonium bromide/didodecyldimethylammonium bromide (3/2, w/w). Nanoparticles were characterized by X-ray diffraction, transmission electronic microscopy (TEM) and vibrating sample magnetometry (VSM), and consisted of magnetite or a mixture of magnetite and maghemite. The particles have an average diameter of 8 nm with a relatively narrow particle size distribution and show possible superparamagnetic behavior. Noticeably higher yields of precipitate are observed for this new approach in comparison with those typicall obtained using reverse microemulsions.