The thermal treatment of poly (acrylonitrile-co-itaconic acid), (P (AN-co-IA)) and polyacrylonitrile (PAN) under the oxygen atmosphere has a complex mechanism which strongly affects the properties of final product carbon nanofiber. Not only precursor composition but also oxidation treatment parameters play a key role in the achievement of the desired properties of the end product; carbon nanofiber. PAN and P (AN-co-IA) based nanofibers were fabricated via electrospinning technique and later treated at different temperatures to investigate the oxidation procedure in the presence of itaconic acid as a copolymer form. Description of the oxidation (thermal stabilization) route of nanofibers is challenging thus powerful characterization tools such as electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and FTIR-ATR are used for characterization and evaluated dependently. All obtained results are pointed out that; IA addition has a positive effect on the oxidation process in nanoscale in terms of reduction of applied temperature and time compared to homopolymer PAN. Spectroscopic results were also correlated with the equivalent Circuit Parameters of Electrochemical Impedance Spectroscopic Measurements, where oxidation and carbonization stages can be followed easily due to the formation of heterocyclic and conjugated structures by thermal treatments. (C) 2020 Elsevier Ltd. All rights reserved.