A new ABA-type triblock copolymer was synthesized by coupling reaction of anhydride and amine-functionalized telechelic polymers. The two blocks of the copolymer, polystyrene end-functionalized with anhydride group (PS-anh) and poly(arylene ether sulfone) functionalized with aromatic amine groups at the termini (PAES-amn), were synthesized by living, anionic and condensation polymerization, respectively. The block copolymer was characterized by size exclusion chromatography (SEC), thermal (DSC and TGA) studies, and the morphology investigated by atomic force microscopy (AFM) and transmission electron microscopy (ITEM). The microstructure of the block copolymer was affected by the volume fraction of the constituent blocks.