Our objective was to prepare a novel series of four-polymer blend proton exchange membranes (PEMs) which could be used in PEM fuel cells (PEMFCs). They were fabricated by the blending of four sulfonated poly(aryl ether sulfone) s (SPAES) copolymers, SPAES-20, SPAES-30, SPAES-40 and SPAES-50 with sulfonation degree (DS) of 20%, 30%, 40% and 50%, respectively. Because of the step by step changes in DS of polymers in the fourpolymer blend membranes, single-phase solutions were formed and converted into transparent and flexible membranes readily. The blend modification endowed the obtained membranes considerably improved dimensional, thermal, hydrolytic and oxidative stabilities, together with good methanol resistance at similar ion exchange capacity (IEC) level while comparing with the control membranes. Among the blend membranes, the B4 (0.5: 1: 2: 2) membrane showed the highest proton conductivity (203.1 mS cm(-1) at 90 degrees C and 169.2 mS cm(-1) at 94.1% RH) with excellent oxidative (5.1% mass loss in Fenton's reagent at 80 degrees C for 1 h) and dimensional stability (< 15% at 80 degrees C). In the H-2/O-2 fuel cell operation, its maximum power output achieved 467.98 mW cm(-2) at 1050 mA cm(-2). The SPAES blend membranes are promising for application in the PEMFCs.