Precipitation was accomplished at 80 degrees C for magnetic nanoparticles in bicontinuous microemulsions that were stabilized with different concentrations of a surfactants mixture of dodecyltrimethylammonium bromide/ didodecyldimethylammonium bromide ( 3/ 2, w/ w). These nanoparticles were characterized by X- ray Diffraction, Scanning Transmission Electronic Microscopy ( STEM), and Vibrating Sample Magnetometry ( VSM), which demonstrated that they were composed of magnetite or a mixture of magnetite- maghemite. The particles were found to have average diameters between 6.9 and 7.9 nm with relatively narrow particle size distribution and showed possible superparamagnetic behavior. In addition, we observed an inverse dependence of particle size on surfactant concentration. Yields obtained in these precipitation reactions were found to be up to three times higher than those typically reported in specialized literature about precipitation of magnetic nanoparticles in reverse microemulsions.