Sulphonated imidized graphene oxide (SIGO) (graphene oxide (GO) tethered sulphonated polyimide) has been successfully synthesized by polycondensation reaction using dianhydride and sulphonated diamine. Polymer electrolyte membranes (PEMs) are prepared by using SIGO (different wt%) and sulphonated poly(imide) (SPI). Resultant SPI/SIGO composite PEMs exhibit improved stabilities (thermal, mechanical and oxidative) and good water-retention properties (high bound water content responsible for proton conduction at high temperature by internal self-humidification). Incorporation of covalent bonded SIGO into SPI matrix results hydrophobic hydrophilic phase separation and facile architecture of proton conducting path. Well optimized sulphonated poly(imide)/sulphonated imidized graphene oxide (15 wt%) (SPI/SIGO-15) composite membrane shows 2.24 meq g(-1), ion-exchange capacity (IEC); 1138 x 10(-2) S cm(-1) proton conductivity; 5.12% bound water content; and 10.52 x 10(-7) cm(2) s(-1) methanol permeability. Maximum power density for pristine SPI membrane (57.12 mW cm(-2)) improves to 78.53 mW cm(-2) for SPI/SIGO-15 membrane, in single-cell direct methanol fuel cell (DMFC) test at 70 C using 2 M methanol fuel. Under similar experimental conditions, Nafion 117 membrane exhibits 62.40 mW cm(-2) maximum power density. Reported strategy for the preparation of PEMs, offers a useful protocol for grafting of functionalized inorganic materials with in organic polymer chain by imidization. (C) 2015 Elsevier B.V. All rights reserved.