The nanocomposite formation in ethylene/propylene/diene rubber (EPDM) mixed with montmorillonite modified with octadecylamine (MMT-ODA) was investigated. The rubber formulation used proved to be critical for the final materials' properties. The combined action of the curatives and glycidyl methacrylate (GMA), which was grafted on the EPDM, resulted in better intercalation and enhanced mechanical behavior of the rubber nanocomposites.