Some of the perovskite oxides such as La0.7Sr0.3CoO3sintered at 1150 °C can have the function, when used as cathode materials in sealed‐off CO2lasers, to improve both output power and operating life. While the output power of the order of 50 W/m has become obtainable in sealed‐off tubes, the longest life observed was 4400 h. It has been shown that this improvement comes from the simultaneous presence of the following properties in some perovskites, of oxygen emissivity, catalytic activity, metallic conductivity, and low sputtering rate.