A series of selectively sulfonated polystyrene-b-poly(ethylene-r-butylene)-b-polystyrene copolymers (SSEBS) with varying degree of sulfonation were synthesized. The morphology of SSEBS characterized by AFM and TEM showed the microphase separated nano-structures. The SSEBS formed nano-sized ionic channels by association of the sulfonate groups in the styrene blocks of SEBS. The well-ordered ionic channels are continuously linked, which resulted in enhanced proton conductivity. Proton conductivity values of SSEBS determined by membrane electrical resistance (MER) measurement was more than that of the commercially available proton exchange membranes. (C) 2004 Elsevier Ltd. All rights reserved.