AbstractA series of membranes, based on sulphonated poly(ether ether ketone) (SPEEK)/polyimide (PI) blends, was prepared at different casting conditions. They were characterised by SEM, FTIR, DMTA, DSC, TGA, water/methanol pervaporation and impedance spectroscopy. The membranes prepared at 130 °C from blends with 10, 20 and 30 wt.-% of PI are homogeneous, and the methanol permeabilities decreased from 28 × 10-10 kg m s-1 m-2 (plain SPEEK) to 7.21, 2.61 and 0.55 × 10-10 kg m s-1 m-2, respectively. This corresponds to a 4- to 57-fold methanol crossover reduction. With this improvement, by the introduction of PI, the power density of SPEEK-based membranes in DMFC tests could be greatly improved.