Sulfonated graphene oxide (SGO) was synthesized by direct esterification reaction between graphene oxide (GO) and hydroxylated sulfonated poly(ether ether ketone) (SPEEK-OH) and then incorporated into sulfonated polyarylene ether nitrile (SPEN) to explore the effect of varying loading on performances of proton exchange membranes. It was found that SGO are uniformly dispersed and form perpendicular packing structure in matrix, triggering the formation of continuous and long-range proton transfer channels and effectively improving proton conductivity. Meanwhile, the water uptake, swelling ratio and methanol permeation are lowered to the corresponding composite PEM compared to pristine SPEN membrane. All of these are attributed to the formation of strong interfacial interaction between SPEN and SGO. As a result, the composite membranes possesses higher selectivity than pristine SPEN. Specially, the composite membrane contained 2 wt% SGO show the lowest swelling ratio at high temperature (just 13.77% at 80 degrees C) and the highest proton conductivity of 0.183 S.cm(-1) at 80 degrees C. Our investigation indicates the great potential of SGO in fabricating composite PEMs and also provides a new approach for the development of PEMs. (C) 2018 Elsevier Ltd. All rights reserved.