The influence of surface acid-base properties on the formation of a dispersed platinum phase on a carbon support was studied by various physico-chemical techniques, i.e., potentiometric titration (ZPC), FT-IR, TPD and XPS. The series of events occurring during thermal activation of Pt/C catalysts was investigated and the results were related to the electrochemical active surface area (MSA) determined by cyclic voltammetry in phosphoric acid. The results suggest that surface acidic oxygen-containing functional groups may act as anchoring centres for the metal particles limiting their growth in the low-temperature range. This effect produces a strong metal-support interaction which affects the electronic nature of platinum sites. In the high-temperature range, basic functional groups are mainly individuated, i.e., Cpi- and pyrone-type sites. Pyrone groups behave similarly to the acidic groups whereas Cpi groups possess an electron-releasing behaviour producing a lower level of metal-support interaction.