The sulfonated poly(ether ether ketone ketone)/phosphotungstic acid (SPEEKK/PWA) composite membranes were researched for proton exchange membranes. The effect of casting condition on the properties of membranes was studied in detail. The study showed that the casting condition has great influence on the membrane properties because of the hydrogen bond between the SPEEK and PWA and the interaction between the SPEEKK and dimethylformamide (DMF). The PWA particles are well crystallized on the surface when the velocity of the solvent volatilization is very slow under the SEM. The study will favor further research on excellent composite membranes for proton exchange membrane fuel cells. (c) 2006 Wiley Periodicals, Inc.