During the electrochemical intercalation and deintercalation processes of sulfuric acid into graphite, the electrical resistivity along the graphene layers was followed with a contactless method. At 20°C, the intercalation process is associated with a large decrease of resistivity; the lowest values are observed for stages 8 to 5 formation, and remain nearly constant until stage 1. However, the intercalation reaction is limited by the oxidation of sulfuric acid and by graphite overoxidation; these effects appear for an apparent charge transfer of C + 1 0 . Between 190 and 300°C (1 or 1000 bar), pure sulfuric acid intercalates readily into graphite without external chemical or electrochemical oxidation. The formation of sulfate GIC is related to the decomposition of H 2 SO 4 progressively evolving sulfur trioxide, which is a powerful oxidizing agent. Oxidation reaction, increasing with temperature above 250°C, is expressed by the apparition of corrosion holes. The samples have been characterized by X-ray diffraction, resistivity measurements, and scanning electron microscopy.