In this work, hydroxylated HPEEK [poly (ether ether ketone)] was covalently grafted on to graphene oxide (GO) sheets and methodically characterized using F1'IR, TEM and XPS. The epoxy composites with GO and HPEEK grafted graphene oxide (HPEEK-g-GO) were prepared using mechanical stirring coupled with a bath sonicator to improve the dispersion and were subsequently cured at 80 degrees C and 180 degrees C. With the addition of only a small amount (0.5 wt%) of HPEEK-g-GO, an impressive 42% increase in storage modulus, 65% enhancement in hardness and 31% increase in fracture toughness was observed with respect to the control epoxy sample. In addition, significant enhancement in tensile strength by 7% was realized in epoxy composites containing 0.5 wt % of HPEEK-g-GO. This improvement in structural properties was attributed to reinforcement by HPEEK-g-GO having sound interface with epoxy. The epoxy composites containing HPEEK-g-GO also showed improvement in glass transition temperature along with the thermal stability up to 300 degrees C. (C) 2017 Elsevier Ltd. All rights reserved.