Trifluoromethanesulfonic acid or triflate acid, chemical formula CF3SO3H, is regarded as one of the strongest acids and resembles Nafion (R) in structure. Erbium triflate, a lanthanum salt of triflate, is thermally stable. This paper reports data on the formation of membranes by the fixation of erbium triflate salts (ErTfO) into the Nafion structure. Five different loadings of ErTfO were used to fabricate ErTfO/Nafion composite membranes and these were characterized, extensively for possible use in direct alcohol fuel cells. The membranes were characterized using XRD, TGA, FTIR, and for mechanical strength, water uptake, ion exchange capacity, alcohol uptake, swelling, proton conductivity alcohol permeability and oxygen stability. The ErTfC/Nafion composite membranes reduced alcohol permeability by 77-80%. The proton conductivity of 3% ErTfO/Nafion composite membranes was 38% higher than that of a pure cast Nafion membrane. The oxygen stability of the ErTfO/Nafion composite membranes was higher than pure cast Naflon. However, the mechanical strength of 7% and 9% ErTfO/Nafion was lower than that of pure cast Naflon. The composite membrane was chemically stable and has potential for use in direct alcohol fuel cells. (C) 2008 Elsevier B.V. All rights reserved.