Hydrophilization of carbon nanofibers (CNFs) was achieved using plasma polymerization of acrylic acid. Transmission electron microscopy (TEM) and spectroscopy techniques were used to assess the structural changes and type of chemical groups grafted on CNFs during plasma treatment. Electron energy loss spectroscopy analysis showed a decrease of sp² bonds and an increase of sp³ bonds coming from the thin film of polyacrylic acid deposited on CNFs during the plasma treatment. X‐ray photoelectron spectroscopy (XPS) corroborated that the sp²/sp³ ratio of the treated CNFs decreased from 3.95 to 1.14. Also the presence of carbonyl and carboxyl groups were identified by XPS, whose presence promotes the hydrophilic character of CNF_S and their dispersion in water. An amorphous structure on the surface of treated CNFs, which corresponds to the nanocoating of polyacrylic acid deposited by plasma, was observed by TEM.