MgO thin films were prepared on soda-lime glass substrates by the radio frequency magnetron sputtering using a MgO target at various oxygen gas flow ratios [O-2/(Ar+O-2)] in order to understand the relationship between MgO film properties and discharge characteristics. The gas discharge property of alternating current plasma display panels (ac PDP) was found to strongly depend on the crystallinity, surface morphology, and contamination with hydroxyl groups, as well as film stoichiometry. The MgO films had a tendency to form structures with a preferred growth orientation of (200) planes with an increasing oxygen gas flow ratio [O-2/(Ar+O-2)] to 0.1. The MgO films were also observed to be fully stoichiometric at an oxygen gas flow ratio [O-2/(Ar+O-2)] of 0.1 The fully stoichiometric MgO films were found to have a minimum in surface roughness and amount of hydroxyl groups and a maximum in grain size. The ac PDP with fully stoichiometric MgO films also showed lower firing and sustaining voltages than those with either magnesium-rich or oxygen-rich MgO films. This was largely attributed to the larger grain size and the reduced hydroxyl groups in the films.