Oxygen reduction reaction (ORR) activity of carbon nitride (CNx) dispersed in polyacrylonitrile (PAN) nanofibers found to improve due to addition of fillers: carbon black (CB) and Nafion (R) dispersion. Size and morphology of as synthesized CNx/PAN/CB/Nafion (R) nanofibers were studied using scanning electron microscope and transmission electron microscope. X-ray photoelectron spectroscopy was carried out to understand the form of N group present in CNx/PAN/CB/Nafion (R) nanofibers. Improvement in ORR activity of CNx/PAN/CB/Nafion (R) was studied using cyclic and linear sweep voltammetries. In order to understand ORR mechanism on CNx/PAN/CB/Nafion (R) nanofibers, RRDE and in-situ FTIR coupled with linear sweep voltammetry was carried out. RRDE experiments confirmed occurring of 4-electron pathway mechanism for ORR and FTIR studies confirmed the dominance of ORR in the active potential range by showing the increase in water content. The stability of CNx/PAN/CB/Nafion (R) nanofibers towards ORR was confirmed by 6000 repetitions of linear sweep voltammetry coupled with FTIR with insignificant reduction in peak current density after 3000 repetitions and stable onset potential after 4000 repetitions. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.