In order to fabricate a high performance triple-phase-boundary (TPB) for a mixed potential type NOx sensor based on stabilized zirconia and oxide electrode, a porous surface of the yttria-stabilized-zirconia substrate (YSZ) was formed with pore-formers (PMMA, graphite and starch) using coating technique. SEM observation result indicated that the porous morphology in the final ceramic was related to the category and amount of the pore formers, so that the pore size and microstructure of YSZ layer could be controlled. The NO₂gas sensors using above-mentioned modified YSZ substrate with porous surface and nano-structured NiO electrode were fabricated and evaluated. The electric potential difference (Delta V) of the sensors varied almost linearly with the logarithm of NO₂concentrations in the examined range of 10-500 ppm at 800℃. The sensor based on 10 wt% starch-added YSZ matrix showed the largest response with the Delta V of 114 mV to 100 ppm NO2. It was also seen that the sensors showed good response-recovery transient, selectivity and repeatability to NO₂.