Novel sulfonated poly(ether ether ketone ketone)s were prepared directly by nucleophilic polycondensation. They showed excellent thermal stability and good solubility and could be easily cast into tough membranes. The sulfonated membranes showed swelling of 16.08-26.71% and an ion-exchange capacity of 1.01-1.57. The transport properties of different cations (H+, Na+, and K+) of membranes based on these polymers were evaluated. The potential for ion-exchange membranes looks good. (c) 2005 Wiley Periodicals, Inc.