The sulfonated poly(arylene ether) (SPAE) multiblock copolymers composed of densely sulfonated hydrophilic blocks were designed and fabricated through aromatic nucleophilic substitution reaction. The modified SPAE (mSPAE) membrane showed a well phase separated morphology as revealed by transmission electron microscopy (TEM) studies. The dense sulfonic acid groups in mSPAE lead to higher ion exchange capacity and water uptake, resulting in well phase separated morphology and superior proton conductivity (247.18 mS cm(-1)) compared with the pristine SPAE membrane (95.73 mS cm(-1)) and a commercial Nafion (NRE-212) membrane (111.40 mS cm-1) under fully humid condition at 80 degrees C. The mSPAE membrane showed improved fuel cell performance compared with pristine SPAE and NRE-212 membranes. The mSPAE membrane showed a current density of 1386 mA cm(-2) at 0.6 V under 100% hydrated condition, whereas the pristine SPAE and NRE-212 membranes showed 766 and 1012 mA cm-2 current density under the same condition. A maximum power density of 928 mW cm(-2) was achieved for mSPAE membrane, which was much higher compared with the pristine SPAE (518 mA cm(-2)) and Nafion-212 (688 mA cm(-2)) membranes indicating that mSPAE membrane would be a potential replacement of the Nafion-212 membrane.