Reference electrode powder is an important part, which affect performance of zirconia oxygen sensors. The new reference electrode powders with variations in terms of Cr2O3-Fe2O3 composition and chromium-oxide ratio have been produced by chemical coprecipitation method. The microstructural characterization of the reference electrode powders were conducted using scanning electron microscopy (SEM). Performance of the reference electrode powders was tested in oxygen activity measurements at molten steel under industrial steelmaking practice. The powders produced by the oxide coprecipitation work very well in terms of the EMF reproducibility and of the response time for the low oxygen content measurements. The chemically produced Cr2O3-Fe2O3 powder mixtures very well attach to the Cr particles. This fact gives good electromotive force (EMF) reproducibility with accurate Al response. Elevated Fe2O3 content of the oxide powder reduces the EMF overshoot and improves the measurement accuracy. More positive EMF measurements, lower Al predictions than the chemical analysis and reduced probe accuracy at higher Al contents are obtained with decreasing the oxide content of the reference powder.