Polarization characteristics of Pt-(Sc0.10Ce0.01)Zr0.89O2 (SSZ) cermet cathodes were studied in order to develop new cathodes for reduced temperature solid oxide fuel cells (SOFCs). Several Pt-SSZ cermet electrodes were prepared by mixing Pt and SSZ powders using a high-energy ball mill. A Pt-SSZ cermet cathode on yttria-stabilized zirconia (YSZ) electrolyte achieved high cathodic activity; the cathode interfacial conductivity reached as high as 6.7 S/cm(2) at 973 K and 0.8 S/cm(2) at 873 K. These results suggest that this Pt-SSZ cermet cathode has enough capability at 973 K, but is still not satisfactory at 873 K. This high activity can be obtained by ball milling SSZ/Pt mixture of proper ratios in vacuum and by controlling electrode thickness, sintering temperature, and Ca impurity. These electrodes showed two optima of interfacial conductivity vs. SSZ/Pt ratio and remarkable dependence on cathode thickness. It was considered that the first optimum is based on two-dimensional reaction sites on YSZ electrolyte surface and the second one originates from three-dimensional expansion of reaction sites into the cermet cathode.