<p>Ionic liquids (ILs) have received considerable attention in the development of high temperature proton exchange membrane (HT-PEM) because of their unique ability to help in achieving high conductivity at higher temperature though the issues associated with leaching of ILs at higher temperatures yet to be resolved. In order to overcome this disadvantage, herein, we report the development of cross-linked HT-PEMs designed from phenyl substituted pyridine bridged oxy-polybenzimidazole (Ph-PyOPBI) and cross-linkable polymeric ionic liquid (cPIL). The cross-linking between Ph-PyOPBI and cPIL significantly improved the phosphoric acid (PA) uptake and proton conductivity of the resulting HT-PEMs. The cross-linked membranes were prepared with 10%, 20%, 30%, 40% of cPIL with respect to Ph-PyOPBI polymer weight and their HT-PEM properties were studied. All the four cross-linked membranes were found to be completely stable in 85% PA while the pristine Ph-PyOPBI membrane was stable only up to 75% PA. The reason for such remarkable stability of cross-linked Ph-PyOPBI in high acid concentration is due to the cross-linking interactions with the cPIL. The membrane containing 10% cPIL exhibited a proton conductivity of 0.053 S cm^–1 at 160 °C which is higher than the pristine Ph-PyOPBI membrane (0.015 S cm^–1 at 160 °C).</p> Graphical abstract <p>Proton Exchange Membrane (PEM) with improved properties for the use in high-temperature PEM fuel cell has been developed by cross-linking the pyridine-bridged polybenzimidazole chains through a cross-linkable polymeric ionic liquid.</p> <p></p>