CO2 sensor was used only one solid electrolyte in many cases. To improve the sensing characteristics of CO2 sensors, solid electrolyte CO2 sensor has been developed by bi-electrolyte type sensor using Na-Beta-alumina and YSZ. However, in many further studies, bielectrolyte type sensor was made by pellet pressed by press machine and additional treatment for formation of interface. In the aspect of mass production, using thick film and additional treatment is not suitable. In this study, CO2 sensor was fabricated by bi-electrolyte structure which was made by an NBA paste layer deposited on YSZ pellet and fired at 1650oC for 2 hour. The formation of stable interface between YSZ and NBA were confirmed by SEM image. When the type IV electrochemical cell arrangement represented by CO2,O2,Pt| Li2CO3-CaCO3||NBA||YSZ|O2,Pt is used to measure the CO2 concentration in air. This sensor EMF should depend only on the concentration of CO2 by logarithmic. Also, sensor shows PCO2 and EMF relationship like nerstian reaction at a temperature of 450oC.