MgO films have been suggested as the protective layer for alternating current plasma display panels, which play significant roles in preventing the failure of the dielectric layer from sputtering by ions, in lowering the firing and sustain voltages due to a higher secondary electron emission coefficient (gamma), and in allowing higher optical transmittance. To investigate the structural and optical properties of the MgO protective films, MgO thin films were deposited on glass substrates by vacuum arc deposition with a magnesium metal target at various oxygen gas flows. To measure the erosion rate of the MgO protective layers, an acceleration test method was used, namely, the Ar+ ion beam-induced erosion test. The effect of moisture on the optical transmittance of the MgO protective layers was also examined. It was found that the optical transmittance decreased with the relative humidity. X-Ray diffraction and AFM have also been used to study the behaviors of the structure and surface morphology. (C) 2003 Elsevier B.V. All rights reserved.