In this research, a novel chromium-iron oxide (Cr2Fe6O12) nanoparticle with rhombohedral symmetry was prepared by a simple thermal treatment method. Heat treatment was conducted using an electric cylinder furnace in an air atmosphere at temperatures between 773 and 923 K, where the produced chromium-iron oxide nanoparticles had different crystallite sizes ranging from 9 to 20 nm. The products were well characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), and X-ray analysis (EDXA).The samples demonstrated a magnetic behavior which was confirmed by using vibrating sample magnetometer (VSM).