Polybenzimidazole (PBI) copolymer containing hydroxyl functional groups was synthesized in this study. Two series of cross-linked PBI membranes have been prepared based on the copolymer with two different crosslinkers reacted with the hydroxyl groups on the PBI main chain. The resultant membranes were investigated in terms of oxidative stability, thermal properties, mechanical properties, and proton conductivity. The mechanical and thermal properties were enhanced in the cross-linked membranes compared to the non-cross-linked membrane. In addition, the thermal degradation temperature of the membranes increased with increasing degree of cross-linking. The Fenton's test was used as the reference of the oxidative stability of the membranes. It was found that cross-linking led to a significant improvement in oxidative stability of the membranes. The proton conductivity of phosphoric acid doped cross-linked PBI membranes could reach 8 x 10(-3) Scm(-1) at 160 degrees C. (C) 2013 Elsevier B.V. All rights reserved.