The measurement of manganese concentration in liquid iron without sampling is a challenge for better production control and improving the efficiency of the steelmaking process. An electrochemical sensor was developed to address this issue. As a crucial component of the sensor, the MnO, which functions as the auxiliary electrode material, was mixed with PVA water solution and deposited on the raw magnesia-doped zirconia tube, and thereafter annealed under an argon atmosphere at 1600 degrees C. The X-ray diffraction indicates the MnO coating remains intact after sintering, and scanning electron microscopy shows the MnO layer tightly adheres to the solid electrolyte. The performance of the galvanic cell is appreciably affected by the particle size of the MnO powder, in the case of fine powder, steady cell potentials can be obtained quickly after immersion into the molten iron. The electromotive force of the cell is inversely proportional to the Mn content, and a linear equation between the two was derived. Furthermore, the relationship between the calculated Mn activities and the Mn concentrations determined by chemical analysis implies a positive deviation from Henry's law, which may chiefly arise from the fact that the MnO activity is less than unity. Additionally, the ionic conductivity of 8mol% Mg-PSZ and the activation energy were also investigated. (c) 2018 Elsevier Ltd. All rights reserved.