Using cyclic voltammetry, impedance spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray fluorescent analysis (XFA), the electrochemical behaviour of glassy carbon (GC) in super-acid media (fluorosulphuric acid FSO3H and trifluoromethansulphonic acid CF3SO3H) was studied. It was found that electro-oxidation of GC in FSO3H leads to chemical modification of the GC surface by fluorosulphate groups owing to the chemical interaction of electrochemically generated peroxydisulphuryldifluoride with the GC electrode. The anodic polarization of GC in CF3SO3H does not result in deep oxidation of its surface because modifying oxidizers in the region of CF3SO3- anion discharge are absent.