The MgO-CaO composites films were prepared by e-beam evaporation to improve both operating voltages and memory coefficient of a protective layers for AC plasma display panels (PDPs). The effects of CaO addition to the conventional MgO films on both the electrical properties and the structural changes of the Mg1-xCaxO thin films deposited on the slide glass substrates were investigated. Atomic force microscopy (AFM) results revealed that the Mg0.8Ca0.2O film had a very rough surface due to the formation of a second phase on the surface. By adding controlled amount of CaO, the Mg-Ca-O films showed a firing voltage of 176 V that is lower than that of the conventional 100% MgO film. The deposition rates of 40-100 nm/min were obtained as a function of [CaO/(MgO + CaO)] ratio of the evaporation source materials.