Abstract: Catalyst combustion sensors are used for detection and analysis of flammable gas and they are widely used in many fields. In order to find out the common failure modes of NC-170S catalyst combustion sensors developed by Nemoto, life data analysis, appearance inspection, X-Ray analysis, and SEM/EDS analysis were carried out. The results show that stress breaking of platinum wire, poisoning of catalyst by silicon, and corrosion of electrode by sulfide are the main failure modes. Specific actions were performed towards these failure modes. The production processing and design of software and hardware were improved. Data gathered from the field for more than one year verified the effectiveness of the actions and the reliability was improved.