The integration of an electric propulsion system to the actual vehicle electronic architecture reveals the emphasis of electromagnetic compatibility (EMC). Electromagnetic shielding is one of the compulsory preventions to restrain external electromagnetic interference (EMI) leakage onto electronic devices. Shielding effectiveness (SE) indicates EMI shielding performance of enclosures. The challenge of design limitations for the enclosures forces to investigate alternative studies for improving SE in electric vehicles (EV). This study intends to increase SE without changing enclosure or aperture dimensions inside EV. Graphene has become a popular material in many different areas, thanks to its good conductivity and strong structure. Graphene sheet properties based on electrical characteristics are investigated initially. Then, a rectangular enclosure in which inner surfaces are coated with graphene sheet is designed. The enclosure coated with graphene sheet inside (CGI) is investigated for various configurations. One of them is based on the elimination of graphene sheet on a single inner surface, while the other ones remain as coated. Another one is based on coating a single inner surface with a graphene sheet. SE results obtained by a numerical model are in good agreement with experimental measurements.