In an effort to improve propene (C3H6) selectivity and long-term stability of the mixed-potential-type yttria-stabilized zirconia (YSZ)-based tubular sensor attached with In2O3 sensing electrode (SE), each of the nanosized noble metals (Pt, Ru, Pd, Rh, or Ir) and YSZ powder was added to In2O3 SE. It was found that the addition of nanosized Pt (0.3 wt %) gave considerable improvement in C3H6 selectivity, and the addition of YSZ powder (10 wt %) exhibited great improvement in long-term stability of the sensor. Thus, the sensor attached with composite SE consisting of In2O3, 0.3 wt % Pt, and 10 wt % YSZ was fabricated and its sensing characteristics to C3H6 were examined. As a result, the present sensor exhibited high selectivity and excellent long-term stability to C3H6 at 450 degrees C under the wet condition for the examined period of about 1 month. Based on the results obtained from the measurement of catalytic activity for CO oxidation to CO2, the observation of morphology, and the analysis of composition of SEs, it was speculated that the added Pt nanoparticles could promote the oxidation of CO and H-2 and then improve the C3H6 selectivity, while the added YSZ powder could stabilize the morphology of the SE/YSZ interface and give better long-term stability. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3090168] All rights reserved.