The present study deals with the development of poly ether ether ketone (PEEK) based proton exchange membrane (PEM) having phosphonic acid as protogenic moiety. The synthesis of phosphonated PEEK was carried out in two simpler steps i.e. chloromethylation followed by phosphonation through Michaelis-Arbuzov reaction. The product was further investigated for structural property through FTIR, H-1 NMR, C-13 NMR, P-31 NMR and XRD while thermal properties were analysed by TGA. Other physical properties such as ion exchange capacity, water uptake and proton conductivity were determined for the prepared membranes to execute their suitability as PEM. The presence of phosphonic acid group provides good thermal and chemical stability to the membranes. The high substitution degree (1.11-1.56) achieved in present case was favourable for providing significant proton conductivity of 0.047 S/cm at 120 degrees C under hydrated conditions to the corresponding membranes which entitle them as potential candidate for PEMs in fuel cells at high temperature. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.