The influence of several additives such as CaO, Y 2O 3, SrO, ZnO, Al 2O 3, TiO 2 and ZrO 2 to MgO on the discharge characteristics of AC plasma display panels was investigated as a function of the additives’ content. Among the various additives, the titanium oxide was the most efficient in lowering the discharge voltages of panels which exhibited 13 V lower firing voltages and 19 V lower sustaining voltages than the conventional MgO. The discharge voltages were found to have minimum points at the additives’ content of 0.1 or 0.2 regardless of which additive. Above this point, the discharge voltages gradually increased according to the additive’s content, which resulted from exceeding the solid solution limit of MgO with the appearance of a cracked film surface. The packing density of the evaporated films was increased by addition of the additives in the range of the additives’ content that did not exceed the solid solution limit of the MgO. There was a nearly linear relationship between the refractive index and the discharge voltages. The densification effect by the additives was thought to be the main reason for the decrease in the discharge voltages.