Electromotive force (EMF) transient curves presented that the sensor showed good repeatable response in the humidity environments using ambient atmosphere as the carrier gas at different temperatures. The 90% response time and recovery time were within 40 s and 50 s, respectively. The sensor also presented stable response characteristics in 75.1% RH and 83.6% RH humidity environments using N(2), 5% O(2), and 50% O(2) as the carrier gases, respectively. The EMF always increased with the partial pressure of oxygen in certain relative humidity. However, the ΔEMF was decreased with the increase of O(2) content in the carrier gas under the condition of the variation of relative humidity from 75.1% to 83.6%. These phenomena revealed that the sensor was sensitive to water vapor without oxygen in the sample gas and too much water vapor had adverse effect on the response to oxygen. Non-Nernst behavior of the sensor was discussed in detail.