A mixed-potential-type yttria-stabilized zirconia (YSZ)-based tubular sensor utilizing a NiO sensing-electrode (SE) was fabricated and examined, with aspirations of monitoring very low concentrations of volatile organic compounds (VOCs) at the ppb level. It was shown that the present sensor gave higher sensitivities towards each of the six different VOCs (toluene, m-xylene, benzene, ethylbenzene, styrene and formaldehyde) than other gases, such as C3H6, H-2, CO and NO2. Responses to different concentrations of pseudo-total VOC (p-TVOC, composed of gas mixture of toluene, m-xylene and formaldehyde) for the present sensor were also measured. It was found that the present sensor could detect very low concentrations of p-TVOC, lower than the current Japanese guideline value of < 175 ppb. In addition, the present sensor exhibited good accuracy for the measurement of p-TVOC concentration, being comparable to that of a commercial hydrocarbon analyzer. The effect of NiO-SE thickness with respect to gas-sensing characteristics was also evaluated and it was found that a decrease in NiO-SE thickness enhanced the sensitivities to all the gases examined for the present sensor. The sensing mechanism for all VOCs tested was confirmed to be in good agreement with the mixed-potential sensing model. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3573780] All rights reserved.