Proton conducting polymer electrolyte membranes were produced by blending of poly(2,5-benzimidazole) (ABPBI) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) at several stoichiometric ratios with respect to polymer repeating units. The membranes were characterized by using Fourier transform infrared spectroscopy for interpolymer interactions and scanning electron microscope for surface morphology. Thermal stability of the materials was investigated by thermogravimetric analysis. Glass transition temperatures of the samples were measured via differential scanning calorimetry. The spectroscopic measurements and water uptake studies indicate a complexation between ABPBI and PAMPS that inhibited polymer exclusion up on swelling in excess water. Proton conductivities of the anhydrous and humidified samples were measured using impedance spectroscopy. The proton conductivity of the humidified ABP-BJ:PAMPS (1 : 2) blend showed a proton conductivity of 0.1 S/cm, which is very close to Nafion 117, at 20 degrees C at 50% relative humidity. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1193-1198,2011