Sulfonated poly(phthalazinone ether ketone)s with different sulfonation degrees were directly polymerized via N-C coupling reaction. The resulting polymers with inherent viscosity ranging from 0.97 to 1.29 dL/g were characterized by H-1 NMR and elemental analysis. Membranes were obtained by casting 5% solution in DMAc (N,N'-dimethylacetamide) of the polymers at 60 degrees C. Because of their specially designed structure, the membranes of the polymer have excellent thermal and oxidative stability. TGA curves showed that the loss of sulfonic groups occurred at around 300 degrees C. The membranes demonstrated excellent acidic stability; their forms could be maintained for at least 47 h when subjected to Fenton's reagent (30 ppm FeSO4 in 30% H2O2) at 25 degrees C. For the polymer with a sulfonation degree of 2, the highest water uptake of 46% at 80 degrees C and the best proton conductivity of 1.77 x 10(-2) S/cm at 95 degrees C 100% relative humidity were obtained, and a low Ea of 5.6 kJ/mol was calculated.