Two series of novel polysulfone-based ionomers containing pendant sulfonic acid groups (designated as PSf-sph-y and PSf-sna-z) have been prepared using commercially available polysulfone and sulfoaryl monomers. The synthesized ionomers have been characterized by nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. The thermal characterization data show that these polymers are stable up to 210°C in acid form and 270°C in salt form in air. Ion exchange capacity, water uptake, swelling, proton conductivity, and methanol permeability of the membranes have been investigated and compared with those of Nafion 115. The PSf-sna-z membranes bearing highly ionic groups on the flexible side chains show lower water uptake, swelling, and methanol permeability compared