The decomposition activity was measured on nonsymmetric electrochemical cell oxide (cathode) yttria-stabilized zircoma (YSZ) (anode) by applying dc voltage lower then 3.5 V in the temperature range from 550 to 700 degreesC. It was found that covering the Pt cathode by a mixture of oxygen ionic conductor (YSZ) and electronic conductor (NiO) increased the NO decomposition even in the presence of excess oxygen. The microstructure of YSZ-NiO mixed oxide electrodes was investigated depending on the mixed oxide electrode sintering temperature. A strong correlation between the microstructure of the mixed oxide electrode and the conversion rate of NO decomposition was observed and investigated. A mechanism for the NO decomposition is proposed and discussed.