Polybenzimidazole (PBI)/ionic liquid (IL) composite membranes were prepared from an organosoluble, fluorine-containing PBI with ionic liquid. 1-hexyl-3-methylimidazolium trifluoromethanesulfonate (HMI-TO. PBI/HMI-Tf composite membranes with different HMI-Tf concentrations have been prepared. The ionic conductivity of the PBI/HMI-Tf composite membranes increased with both the temperature and the HMI-Tf content. The composite membranes achieve high ionic conductivity (1.6 x 10(-2) S/cm) at 250 degrees C under anhydrous conditions. Although the addition of HMI-Tf resulted in a slight decrease in the methanol barrier ability and mechanical properties of the PBI membranes. the PBI/HMI-Tf composite membranes have demonstrated high thermal stability up to 300 degrees C, which is attractive for high-temperature (>200 degrees C) polymer electrolyte membrane fuel cells. (C) 2010 Elsevier Ltd. All rights reserved..