This study aims to investigate surface catalytic reaction and flame combustion of lean premixed mixture in CST (catalytically stabilized thermal) combustor that consists of a catalyst bed and a thermal combustor. Two types of CST combustor, Pd catalyst (one stage) and Pd/Pt catalyst (two stages), were tested. After surface ignition, two systems showed different behaviors in the temperatures of the catalyst bed. The temperature of Pd catalyst system remained at almost the constant temperature, 78O–790°C, insensitive to the preheat temperature. However, the temperature of Pd/Pt catalyst increased steadily with the preheat temperature. Pd/Pt catalyst system had a lower preheat temperature for flame ignition in the thermal combustor than the Pd catalyst system. The lean flammability limit of CST combustor was also investigated. The lean combustion supported by surface catalytic reaction was more stable than flame combustion alone.