Cerium sulfophenyl phosphate (CeSPP) doped polybenzimidazole (PBI) composite membranes were prepared by hot-pressing method as promising candidates for high temperature proton exchange membranes. In order to improve the oxidative stability of the composite membrane (PBI/CeSPP), the active vicinal diamino groups on polymer ends were protected by transformation into benzimidazolones. It was found that the membranes prepared from end-group protected PBI (e-PBI) had an evidently enhanced oxidative stability in comparison with the membrane made from unprotected PBI (u-PBI). CeSPP was found to be well dispersed in the polymer matrix due to its organic-inorganic nature and the strong ionic/hydrogen bonding between PBI and it. The composite membrane exhibited good mechanical strength and thermal stability up to 200 degrees C. The temperature and relative humidity dependence of the proton conductivity was investigated. The proton conductivity of e-PBI/CeSPP (25 wt%) at 180 degrees C reached 0.11, 0.039 and 0.0024 S cm(-1) at 100%, 50% and 0 relative humidity, respectively. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.