Mixed potential ammonia gas sensors were fabricated by using two sensing materials of Ni₃V₂O₈ and Au-V₂O₅ as working electrodes, YSZ as electrolyte and platinum as reference electrode. The results have shown that the Ni₃V₂O₈ sensors show cross-sensitivity toward NO gas. However, Au-V₂O₅ working electrodes displayed a high sensitivity to NH3 as well as very fast response and recovery times at high temperatures. Furthermore, the results indicate that the selectivity of Au-V₂O₅sensors increases by increasing temperature.