In this research,a novel chromium-ironoxide (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), X-ray analysis (EDXA), and Fourier transform infrared spectroscopy (FT-IR). The samples demonstrated a magnetic behavior with unpaired electron spins, which was confirmed by using vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR) spectroscopy.