This paper reports performance characteristics of an electrochemical sensor for CO2 monitoring. The sensor is based on yttria-stabilised (10 mol% Y2O3) cubic zirconia (as a solid electrolyte) and equipped with a CO2 sensing electrode (made of the mixture of carbonates), and Pt reference electrode exposed to air. The sensor performance at 691.6 K is characterised by a stable sensing signal within 5 months. Its response time is 60 s.