In this study, we investigated the heat treatment temperature effect on the morphology and oxygen reduction reaction activity of carbon-supported Pd-Co alloy electrocatalysts. As prepared Pd-Co bimetallic nanoparticles showed a single-phase face-centered cubic disordered structure, and the mean particle size decreased with a Co content. In order to improve activity and stability, the catalysts were heat-treated in a temperature range of 300 to 700 A degrees C. From the results of oxygen reduction reaction activity tests, the optimal heat treatment temperature was found to be 700 A degrees C for the low Co content samples, while 300 A degrees C was the best condition for the high Co content samples.