Pt/C is widely used as a PEFC electrocatalyst. However, Pt detachment and aggregation due to carbon support corrosion can occur. Therefore, the conventional Pt/C electrocatalyst has a difficulty in durability. We have developed Pt-based electrocatalysts dispersed on graphitized carbon black (GCB) coated with SnO2 thin layer support, achieving both high activity and high durability. Here in this study, Pt-Co alloy based electrocatalysts,Pt3Co/Sn0.98Nb0.02O2/GCB, are prepared. XRD measurement confirmed that the catalyst was supported on the oxide. STEM analysis confirmed the alloying of Pt with Co. The catalytic activity was characterized by half-cell electrochemical measurements. The electrochemical activity and pore structure were examined by preparing membrane electrode assemblies (MEA) usingPt3Co/Sn0.98Nb0.02O2/GCB as the cathode catalyst.