This study investigated the effect of supporting electrolytes with different molar ratios of inorganic (KCl) and organic salt (pTSA) on antioxidant activity of polyaniline/reduced graphene oxide (PAni/r-GO) nanocomposite electrosynthesized on composite 2B graphite pencil in 1 M H3PO4 to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) free radicals. The synthesis of PAni/r-GO nanocomposite was accomplished by cyclic voltammetry. The FT-IR and the electrochemical impedance spectroscopy (EIS) confirmed that the presence of KCl in the medium increased the degree of conductivity of polyaniline. In addition to this, the charge transfer resistance (Rct) value of synthesized composite in the presence of KCl is much smaller than that synthesized in the presence of pTSA; besides, the UV-vis spectra demonstrated the antioxidant activity of composite through reaction with free radicals in methanol solution. This indicated that both DPPH and ABTS eliminate increase in the presence of PAni/r-GO nanocomposite electrosynthesized with pTSA. Thus, scavenging of DPPH and ABTS radicals becomes more efficient when the amount of pTSA supporting electrolyte in the synthesis of PAni/r-GO nanocomposite is increased. (C) 2015 Elsevier B.V. All rights reserved.