Ionomeric composites based on sepiolite and hydrogenated poly(styrene butadiene) block copolymer were obtained and characterized from a microstructural and electrical point of view. Before blending, because of the high silanol group concentration in the sepiolite, the latter could be organophilized with suitable coupling agents. The resulting materials were easily processed into thin films or membranes 0.2-0.4 mm thick, their conductivity in some cases approaching 10(-1) S/cm. Their suitability for film formation and good electrical properties indicate potential applications as electrolytes in polymer fuel cells.