Carbon nanostructures (CNS) with high specific surface and porosity prepared by high energy ball milling of graphite is considered as one of the potential alternatives to Vulcan as catalyst support for polymer electrolyte membrane fuel cells. Purification and functionalization of as-prepared CNS were carried out in a single-stage reflux with different proportions and concentrations of the oxidizing mixture, H2SO4 and HNO3. The density of the generated surface functional groups were investigated by XPS based on the activity of platinum dispersed on the specific sites of CNS. Cyclic voltammetry studies revealed that the electrochemical performance for some of the surface modified PUCNS were found to be similar to commercial ETEKO with 20 wt.% Pt supported on Vulcan XC-72 carbon black. XRD and HRTEM were also used to investigate the shape, size and distribution of Pt clusters on the functionalized surface of these CNS. (c) 2006 Elsevier Ltd. All fights reserved.