Graphene oxide (GO) included polyacrylonitrile (PAN) composite electrospun nanofiber webs were fabricated, and thermal oxidation of PAN/GO composite nanofibers were performed at different temperatures (25, 250, 280, and 300 degrees C) for different time intervals (0, 1 and 3 h.) to investigate the oxidation process of PAN/GO nanofibers. The thermal oxidation process of PAN has a complex mechanism through the cyclization and dehydrogenation steps. For all oxidized samples, Electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR) Spectroscopic results were comparatively evaluated to investigate the effect of GO addition onto the nanofiber webs. After heat treatment, change in C1s spectra from virgin PAN to oxidized form was detected and sp(2) carbon is developed. The presence of GO accelerated the oxidation and development of the final structure. At shorter heat treatment time, less oxidized forms are obtained. The cyclization of nitrile pendant groups of PAN forming polyimine type structure is the main reaction occurs during stabilization. In addition to the imine sequences with three to six units long, the presence of polar groups C=O, OH and COOH in the chains facilitates the initiation of the cyclization process through a nucleophilic attack and accelerates the subsequent oxidative ring closure reactions which these newly formed bonds during thermal oxidation and stabilization steps play an essential role on the carbonization process as an intermediate form of PAN based structures.