The present invention relates to a process for preparing electrode catalyst materials for a polymer electrolyte membrane fuel cell (PEMFC), and particularly to a high-performance platinum-non-platinum mixed electrode catalyst (Pt—RuOs/C) having a physically mixed structure of RuOs alloy and platinum materials, which is prepared by adding a small amount of platinum (Pt) to RuOs alloy materials highly dispersed on a carbon support, where the amount of platinum used is drastically reduced as compared to the conventional platinum materials, thus lowering the manufacturing cost.