||For wide spread commercialization of proton exchange membrane fuel cells, proton conducting membranes are one of the key components. While perfluorinated sulfonic acid (PFSA) polymers (e.g. Nafion) are state-of-the-art, there has been a great demand for alternative membranes with non-fluorinated structure in terms of cost, gas-permeability, and environmental compatibility. In the last couple of years, we have designed and synthesized the multiblock copolymers which contain rigid sulfonated aromatic chains as hydrophilic blocks so as to have high proton conductivity and chemical stability, and linear flexible aromatic chains as hydrophobic blocks so as to have good mechanical properties. The investigated hydrophilic blocks include sulfonated phenylene, sulfonated phenylene sulfone, and sulfonated phenylene sulfide sulfone. Synthesis, membrane morphology, water uptake, proton conductivity, mechanical strength, fuel cell performance, and durability will be discussed.