This paper addresses issues surrounding the design of the proton exchange membrane for fuel cells, and more specifically, the role of the polymer architecture on the proton conductivity and gas permeability. In this study, we describe the syntheses and characterizations of sulfonated block, graft, random-graft, and block-graft copolymers. The proton conductivity and oxygen permeability of the novel sulfonated block-graft copolyimide, S-bg-PI, showed 0.44 S cm −1 at 80 °C and 98%RH and 3.2 × 10 −12 cm 3 (STP) cm/(cm 2 sec cmHg) at 35 °C and 76 cmHg, respectively, while those of Nafion indicated 0.15 S cm −1 and 1.1 × 10 −10 cm 3 (STP) cm/(cm 2 sec cmHg) under the same conditions, respectively. The apparent selectivity ratio calculated from the proton and oxygen transports of S-bg-PI was 103 times larger than that determined in Nafion, indicating that the novel sulfonated block-graft copolyimide membrane has excellent properties for fuel cell applications.