Abstract High styrenic sulfonated polystyrene-block-poly(ethyl-ran-propylene)-block-polystyrene (S-polySEPS) containing 65% styrene groups was prepared by sulfonation at the phenyl group. Also, S-polySEPS/clay composite film was produced by mixing organic clay with S-polySEPS in organic blending solvent (THF/DCE/IPA). The proton conductivity of the pure S-polySEPS film and S-polySEPS/clay composite films was ranged from 10−2 to 10−1Scm−1. In particular, the S-polySEPS/clay 1wt% composite film was shown higher proton conductivity, higher ion exchange capacity (IEC) and lower water uptake than Nafion® 117 membrane. However, the proton conductivity of the S-polyseps/clay composite films slightly was decreased with increasing the contents of organic clay. Thermogravimetric analysis (TGA) was carried out to investigate the thermal stability of S-polySEPS/clay composite films. The 1H NMR and FT-IR analysis is used to verify the sulfonation reaction on the phenyl groups of S-polySEPS. The micro-phase separated images and dispersed organic clay state of the prepared films were confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD).