The effects of an addition of ZrO2 on the microstructure and electrical properties of MgO films as a protective layer for AC plasma display panels were investigated. MgO + a 200 ppm ZrO2 protective layer prepared by e-beam evaporation exhibited a secondary electron emission coefficient (γ) that was improved by 21% compared to that of a pure MgO protective layer. The relative density and Vickers hardness increased with a further addition of ZrO2. These results suggest that the discharge properties and optical properties of MgO protective layers are closely related to the relative density and Vickers hardness. The good optical and electrical properties of γ, at 0.080, a grain size of 19 μm and an optical transmittance of 91.93 % were obtained for the MgO + 200 ppm ZrO2 protective layer sintered at 1700˚C for 5 hrs.