A series of proton exchange membranes based on sulfonated multiblock copolymers with three polysulfone (PSU) and polyphenylsulfone (PPSU) ratios (50/50, 60/40 and 75/25) are prepared following a synthesis strategy that aims to achieve a microphase separation. A selective sulfonation of PSU blocks was observed in copolymers with a high proportion of PSU. The water uptake is higher in these materials (31% and 57% for SPES 50/50 and SPES 75/25, respectively at 60 C) while the tensile strength was lower (56.0 MPa and 40.6 MPa for SPES 50/50 and SPES 75/25 in the H+ form, respectively). Ionic conductivity of SPES 75/25 membranes measured both ex situ and in situ at 80 C is 25 and 31 mS/cm respectively. Fuel cell tests reveal that SPES 75/25 shows the highest value for the maximum power density (670 mW/cm2 at 70 C and 100% of RH) which is higher than that achieved for SPES 50/50 (400 mW*cm2 ). In addition, the high current density obtained for SPES 75/25 (1000 mA/cm-2 at 0.6 V and 70° C) compared with SPES50/50 (600 mA/cm2 ) and Nafion 112 (450 mA/cm2 at 75 °C) shows its promising properties as solid electrolyte in polymeric fuel cells.