Mixed-potential type sensors using different ion conducting electrolytes with a Pt working electrode have been fabricated to investigate a relationship between the sensing properties for hydrocarbons and ion conduction in the electrolyte under oxidizing conditions at 600 degreesC. There was an increase in the mixed potential for propene with increasing proton conduction or decreasing oxide ion conduction. The sensor using a SrCe0.95Yb0.05O3-alpha electrolyte showed an enhanced mixed potential for C1-C4 hydrocarbons by increasing the carbon number, unsaturating the C-C linkage, and branching the chain structure. In addition, this sensor barely showed the mixed potential for hydrogen, carbon monoxide, and nitrogen monoxide.