The electrochemical behavior of NO sensors composed of a partially-stabilized Y2O3-ZrO2 (PSZ) porous electrolyte with 0, 2, 3.8, 5 and 10 wt% Al2O3 additions was investigated using the impedancemetric technique. The addition of Al2O3 modified ionic transport within the electrolyte, and caused the electrode/electrolyte interfacial resistance to increase. NO sensors with a PSZ electrolyte containing 2 wt% Al2O3 demonstrated greater sensitivity to NO under dry and humidified gas conditions, in comparison to the other composite PSZ-Al2O3 based sensors. The 2 wt% Al2O3 addition provided enhance grain boundary conductivity within the PSZ electrolyte, and possibly limited oxygen reactions along the triple phase boundary; thereby, enabling NO reactions to proceed more readily. Impedance spectroscopy measurements of the various PSZ-Al2O3 based NO sensors were collected for different operating conditions in order to interpret the behavior of: 1) the electrical response, 2) interfacial NO reactions, and 3) the NO sensing response due to the addition of Al2O3. (C) The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons. org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse,