Structure-properties relationships in terms of gas transport have been established for a large series of sulfonated copolyimides synthesized with a naphthalenic dianhydride, a sulfonated diamine [SD] and various non-sulfonated diamines. For these two phases systems. a phase inversion has been evidenced for sulfonated block content ranging between 30 and 50%. The contribution of the dispersed sulfonated phase to the gas transport greatly depends on the structure of the non-sulfonated diamine. As a consequence, a large range of permeability values can be obtained varying the nature of the non-sulfonated diamine, the sulfonated diamine content and the sulfonated block length. The diffusion coefficient is in all cases the dominant factor in the transport phenomena and good compromise between O-2/N-2 selectivity and O-2 flux can be achieved with these systems.