Abstract: The dielectric properties of magnetite nanoparticles for different grain sizes with different test frequency f and at different temperature T were investigated. In magnetite nanoparticles the dielectric relaxation follows thermally activated process. The activation energy is obtained around 98 meV for 15 nm particles of magnetite. The observed activation energies varies with decreasing particle size. The observation of a sudden drop in the field-cooled dc magnetic susceptibility (T) curve at 100 K infers that the slope change in dielectric relaxation is related to the occurrence of the Verwey transition in the nanoparticles. It is also shows superparamagnetism which useful for Hyperthermia as well as Magnetic Resonance imaging in Medical Parameters.