We studied how to form an MgO protective layer on an ac-type plasma display panel (PDP) using a screen-printing method. In our study, we focused on high luminous efficiency and low drive voltage. To raise the luminous efficiency, it is necessary to limit the discharge current. The firing voltage (V-t), which is the voltage at which all cells start to discharge, and the sustaining voltage (V-s), which is the minimum voltage required for all cells to sustain discharge, have no clear relationship to luminous efficiency. To attain both a higher luminous efficiency and a lower drive voltage, a thinner more crystalline layer is necessary. We found that we could prepare an MgO layer by screen-printing and sintering fine vapor-deposited MgO powders of different grain sizes with an MgO liquid binder. An MgO protective layer prepared by this method provided both a low drive voltage and superior luminous efficiency 2.8 times higher than that of a sputtered layer. The screen-printing method thus enables larger ac-PDPs to be produced at lower cost.