This work reports the preparation and characterization of new polymeric ionomers based on etylene-propylene-diene copolymer (EPDM) with a high norbornene content. The sulfonation level was determined with X-ray photoelectron spectroscopy, and the microstructural characterization was obtained through differential scanning calorimetry and dynamic mechanical analysis. In addition, the effects of certain plasticizers and polymers on the microstructures and conducting properties of these materials were studied, with special attention paid to the latter because of the interest aroused by these materials as membranes in polymer fuel cells. On the basis of the results, some of the synthesized membranes could be used for fuel cells because of their high conductivity (greater than or equal to 10(-2) S/cm) and good dimensional stability (any shrinkage observed).