A series of ionically crosslinked composite membranes were prepared from sulfonated poly(arylene ether sulfone) (SPAES) and polybenzimidazole (PBI) via in situ polymerization method. The structure of the pristine polymer and the composite membranes were characterized by FT-IR. The performance of the composite membranes was characterized. The study showed that the introduction of PBI led to the reduction of methanol swelling ratio and the increase of mechanical properties due to the acid-base interaction between the sulfonic acid groups and benzimidazole groups. Moreover, the oxidative stability and thermal stability of the composite membranes were improved greatly. With the increase of PBI content, the methanol permeability coefficient of the composite membranes gradually decreased from 1.59 x 10(-6) cm(2)/s to 1.28 X 10(-8) cm(2)/s at 30 degrees C. Despite the fact that the proton conductivity decreased to some extent as a result of the addition of PBI, the composite membrane with PBI content of 5 wt.% still showed a proton conductivity of 0.201 S/cm at 80 degrees C which could actually meet the requirement of proton exchange fuel cell application. Furthermore, the composite membranes with PBI content of 2.5-7.5 wt.% showed better selectivity than Nafion 117 taking into consideration the methanol swelling ratio and proton conductivity comprehensively. (C) 2009 Published by Elsevier B.V.