A series of membranes based on amino-modified polybenzimidazole with grafted ethyl phosphonic acid have been successfully prepared. Firstly, the amino-modified polybenzimidazole (PBI-NH2-X) was synthesized, then the ethyl phosphoric acid (EPA) were grafted on to PBI-NH2-X to obtained amino-modified polybenzimidazoles with grafted ethyl phosphonic acid groups (PBI-NH2-EPA-X). EPA is introduced into the matrix to improve the H3PO4 doping level and proton conductivity of the membranes. The obtained membranes display good dimensional and thermal stability. Long-term stability of the grafted membranes is much better than the pristine PBI membranes. Moreover, PBI-NH2-EPA-15 shows a proton conductivity of 0.062 S cm(-1) at 170 degrees C, which is 342% higher than that of PBI. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.