Solid-electrolyte thick film of NASICON (sodium super ionic conductor) was synthesized through an inorganic reagent based sol-gel process. It was prepared onto an alumina tube substrate by dip-coating method, and then followed sintering at high temperature to get NASICON phase. After Pt contact and reference electrodes as well as complex carbonate Li2CO3-BaCO3 auxiliary electrode were attached, a small-volume thick film CO2 sensor was obtained. Comparing with traditional planar pellet CO2 sensor, the tube-type sensor possessed extra merits such as high heating efficiency, lower power consumption and miniaturized framework. In the paper, some characteristics of the thick film CO2 sensor including sensitivity, selectivity, response and recovery time and stability were investigated in emphasis. (c) 2004 Elsevier B.V. All rights reserved.