Silicon oxynitride (SiOxNy) films have been formed by adding proper amount of oxygen gas to usual forming condition of silicon nitride (SiNx) films in catalytic chemical vapor deposition (Cat-CVD) method. The composition and refractive index of the film can be systematically controlled by changing oxygen flow rate. Organic light-emitting diodes (OLEDs) covered with SiNx/SiOxNy stacked films have been completely protected from damage due to oxygen and moisture and their initial emission intensity is maintained over 1000 hours under 60 degrees C and 90% RH, which is equivalent to 50000 hours in normal temperature and humidity conditions. (C) 2007 Elsevier B.V. All rights reserved.