Removal of nitrogen oxide (NO) by electrochemical reduction was studied using a steam electrolysis cell with platinum electrodes and a proton conductor SrZr0.9Yb0.1O3-alpha as the electrolyte. Without NO, the cell produced H-2 with nearly 100% current efficiency in the temperature range 380-590 degrees C. With NO fed to the cathode, NO was effectively reduced. The main products were N2O and N-2 at low current densities, and N-2 and NH3 at higher current densities. When O-2 was mixed into the cathode gas, NO was not reduced on the pure Pt cathode. However, ’Pt sponge + Sr/Al2O3’ catalyst on the Pt cathode showed a good catalytic ability for the reduction of NO supplied with O-2.