Abstract: Amorphous alumina films were prepared by RF magnetron sputtering with the α-Al₂O₃ as target.The effects of applied RF power and working pressure on the Al₂O₃ films were studied by using X-ray diffraction,scanning electron microscopy,scratching adhesion tester and surface profilometer.The relationships between the dielectric properties of Al₂O₃ films and the applied RF power and the frequency were investigated with impedance analyzer.The results indicate that the surface of the as-grown amorphous alumina thin films is smooth and compact.The dielectric constants and the deposition rate were increased and the dielectric losses were decreased with the increase of the applied RF power.With the increase of the frequency,the dielectric constants at a high frequency become smaller and stable gradually.