Development of protective layers with a higher secondary electron emission yield than that of the conventional MgO is necessary to attain both a lower driving voltage and a higher luminous efficiency in alternating current plasma display panels. Alkaline earth metal oxides, such as SrO and CaO were added to the pure MgO in order to improve the electrical characteristics of the conventional MgO protective layer. With addition of SrO and CaO to MgO, the intensity of the (111) peak remained unchanged but the (311) peak newly appeared in the x-ray diffraction results. The secondary electron emission yield of Mg1-x-ySrxCayO films was found to be larger than that of the MgO film and in particular, the Mg0.7Sr0.2Ca0.1O films showed the largest secondary electron emission yield among the prepared films of the Mg-Sr-Ca-O system in this work. The luminous efficiency of the panel with the Mg0.7Sr0.2Ca0.1O protective layer was also much higher than that of the panel with the MgO protective layer probably due to its lower discharging voltage. The increase in the luminous efficiency and the decrease in the driving voltage were in good agreement with the results of the secondary electron emission yield as expected.