Pd nanoparticles on tin oxide-carbon composite support (Pd/SnO(2)-KB) are synthesized by sequential impregnation and successive reduction method. The Pd/SnO(2)-KB catalyst is reduced at various temperatures and the evolution of phases such as intermetallic Pd(3)Sn compound depending on temperature is characterized with XRD, TEM and XPS analyses. Pd/SnO(2)-KB reduced at 700 degrees C and above temperatures exhibits the Pd-Sn intermetallic compound with a smaller particle size than Pd pure metal phase. Pd/SnO(2)-KB reduced at 700 degrees C shows the highest oxygen reduction catalytic activity, which is attributed to the combined effect of the smaller oxygen binding energy of Pd and the increased oxygen adsorption affinity of Sn on the intermetallic Pd-Sn surface. The approach of improving electrocatalytic activity by forming an intermetallic compound can be attempted with various combinations of noble and transition metals. (C) 2010 Elsevier B.V. All rights reserved.