Novel sulfonated poly(phthalazinone ether ketone) (SPPEK) was synthesized by direct polymerization via N-C coupling reaction. The membrane based on SPPEK was simply obtained by casting from 5% solution of SPPEK in NN-dimethylacetamide (DMAc) at 60 degrees C. The as-made membrane was characterized by ion-exchange capacity (IEC), thermal analysis, proton conductivity, single cell performance and electrochemical impedance spectra (EIS). The SPPEK membrane showed excellent characteristic as a proton exchange membrane (PEM) for PEMFC application, such as high ionic exchange content (IEC) of 2.04 mequiv g(-1), high water uptake of 50.6% at 100 degrees C, the proton conductivity of 1.06 x 10(-2) S cm(-1) at 20 degrees C, as well as the superior anti-hydrolytic ability and mechanical strength. Moreover, the membrane exhibited higher thermal stability than Nafion 115. Cell evaluation experiment demonstrated a better performance of SPPEK than that of Nafion 115-cell. Finally, electrochemical impedance spectra (EIS) was conducted to measure the charge transfer resistance to compare the difference between SPEEK and Nation 115. (c) 2005 Elsevier B.V. All rights reserved.