We are developing direct decomposition catalysts to decompose the NOx involved in high temperature exhaust gases to N-2 and O-2 without any reductants such as urea and plan to bring this technology into practice in the 21st century. We expect to create very simple deNO(x) systems using direct decomposition catalysts applicable to a wide range of fields (co-generation, boilers, automobiles and so on) after overcoming the technical difficulties, Perovskite catalyst and zeolite catalyst are the most promising materials for direct decomposition catalysts. This study focuses on seeking and designing novel NOx direct decomposition catalysts having high activities through theoretical studies using computational chemistry and experimental studies using surface-science techniques.