Abstract The crosslinked polybenzimidazole (PBI) proton exchange membrane is prepared by blending the epoxy (diglycidyl ether bisphenol-A) resin in the PBI with an imidazole–NH/epoxide Eqv. no. ratio ranging from 20/1 to 6/1. We show that the mechanical properties of the PBI membrane are improved by introducing a small quantity of crosslinks in the membranes (i.e., an imidazole–NH/epoxide Eqv. no. ratio of 15/1–10/1). Due to its high mechanical strength, the thinner crosslinked PBI membrane (thickness ∼50 μm) has a similar H 2 /O 2 gas barrier property to the thicker PBI membrane (thickness ∼80 μm). Thus, the proton transport resistance across the membrane thickness direction of the thinner crosslinked PBI membrane is lower than that of the thicker non-crosslinked PBI membrane. We show that the crosslinked PBI membrane has a better fuel cell performance than the non-crosslinked PBI membrane at 160 °C with a non-humidified H 2 gas.