Hydrophilic-hydrophobic alternating multiblock poly(arylene ether sulfone) copolymers containing 4,4'-biphenol (BP) or phenolphthalein (PPH) were synthesized via a coupling reaction between phenoxide-terminated hydrophilic oligomers (BPS100 and PPH100) and highly reactive decafluorobiphenyl end-capped hydrophobic oligomers (BPS0 and PPH0). The block length and block combination of copolymers were varied by precisely controlling the molecular weight M-n and end group functionality of oligomers. The resulting hydrophilic hydrophobic sequenced multiblock copolymers afforded transparent, ductile, and tough membranes by solution casting from DMAc. Membrane properties of these copolymers were characterized including intrinsic viscosity, thermal stabilities, morphology, water uptake, and proton conductivity. Results were compared among copolymers with various block lengths and block types. Proton conductivity measurements revealed that PPH0-BPS100 copolymers having high IEC values showed better performance than copolymers with PPH100 as hydrophilic blocks. Well-defined nanophase separated morphologies of the multiblock copolymers were demonstrated by tapping mode atomic force microscopy (AFM), confirming that the hydrophilic domains provide a pathway for water and proton transport. It was also shown that the volume fraction of hydrophobic/hydrophilic domains, as well as IEC values, played a critical role in determining the morphological structures and thus the proton transport. Preliminary studies on exploring the film drying temperature and annealing effect on the membrane properties were also reported.