The synthesis of sulfonated carbon materials (SCMs) via the direct sulfonation of carbon nanofibers with sulfuric acid in the presence of vanadium compounds is studied. An efficient sulfiding system (98% H2SO4–NaVO3) providing a high sulfur content in a carbon material without oleum is proposed. It is established that the introduced sulfur exists in samples in the form of sulfo groups located predominantly on the surface. No intrusion of sulfuric acid residues between graphene layers with the formation of clathrates is revealed. It is shown that the surface of a carbon material is partially oxidized with the formation of carbonyl and carboxyl groups. The kinetic activity of the synthesized SCMs in the liquid-phase reaction of acetic acid esterification with ethanol is studied.