Highly disulfonated poly(aryl ether ether ketone)s (SPEEK-70) copolymer was synthesized via direct polymerization to precisely control the degree of sulfonation (D-s = 1.40), which was confirmed and estimated by H-1 NMR. As expected, the proton conductivity of SPEEK-70 membrane is 0.084 S/cm at 25 degrees C and increases to 0.167 S/cm at 80 degrees C, surpassing that of Nation (R) 117. However, the relatively high methanol crossover and excessively swelling properties limited its usage in DMFC. Poly(amide imide) was blended with SPEEK-70 to improve the methanol resistance and mechanical properties. These blend membranes were characterized as a function of weight fraction of PAI in terms of ion exchange capacity (IEC), water uptake, water desorption, proton conductivity and methanol permeability in detail. Although the proton conductivities decreased upon the addition of PAI, higher selectivity values defined as the ratio of proton conductivity to methanol permeability were found for the blend membranes. Therefore, the SPEEK/PAI blend membranes are promising for usage in DMFC. (c) 2007 Elsevier Ltd. All rights reserved.