High-temperature oxidation processes of carbon microparticles Vulcan XC72 coated with platinum nanoparticles (Pt/C) were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The presence of different specific temperature ranges in the oxidation of carbon support was shown to be due to both the peculiarities of granulometric composition of carbon black microparticles, different size, and uneven spatial distribution of platinum nanoparticles in the pores and on the surface of the carbon support. The correlation between the length of a section in the thermograms and the fraction of carbon microparticles poorly coated with platinum can be used to analyze the uniformity of Pt nanoparticle spatial distribution in the metal–carbon catalysts and therefore to select electrocatalysts with optimal microstructure. This analysis is expected to be effectively utilized in order to assess the uniformity of platinum distribution on carbon microparticles and also to provide additional information about granulometric composition of carbon supports.