Sulfonated poly(etheretherketone) with a cardo group (SPEEK-WC) exhibiting a wide range of degree of sulfonation (DS) was used to prepare polymeric membranes and composite membranes obtained by incorporation of an amorphous zirconium phosphate sulfophenylenphosphonate (Zr(HPO4)(O3PC6H4SO3H), hereafter Zr(SPP)) in a SPEEK-WC matrix. The nominal composition of the composite membranes was fixed at 20 wt% of Zr(SPP). Both types of membrane were characterized for their proton conductivity, methanol permeability, water and/or methanol uptake, morphology by SEM and mechanical properties. For comparison, a commercial Nation 117 membrane was characterized under the same operative conditions. The composite membranes exhibited a reduced water uptake in comparison with the polymeric membranes especially at high DS values and temperature higher than 50 degrees C. As a result, the water uptake into composite membranes remained about constant in the range 20-70 degrees C. The methanol permeability (P) of both polymeric and composite membranes was always lower than that of a commercial Nation 117 membrane. At 22 degrees C and 100% relative humidity (RH), the proton conductivities (sigma) of the polymeric membranes increased from 6 x 10(-4) to 1 x 10(-2) S cm(-1) with the increase of DS from 0.1 to 1.04. The higher conductivity value was comparable with that of Nation 117 membrane (3 x 10(-2) S cm(-1)) measured under the same operative conditions. The conductivities of the composite membranes are close to that of the corresponding polymeric membranes, but they are affected to a lesser extent by the polymer DS. The maximum value of the sigma/P ratio (about 7 x 10(4) at 25 degrees C) was found for the composite membrane with DS = 0.2 and was 2.5 times higher than the corresponding value of the Nation membrane. (c) 2006 Elsevier B.V. All rights reserved.