We adopted divalent cationic conductor, MgZr4(PO4)6(MgZP), for the first time as the electrolyte of EMF type CO2 gas sensors, having the following cell construction : PtCO2, O2 metal carbonate parallel-to solid electrolyte O-2, Pt. In the case of sodium carbonate (Na2CO3), the sensor showed the Nernstian response to CO2 in pressure range between 1 and 100 KPa at temperatures from 400 to 500-degrees-C within a few minutes.