We successfully fabricated three-dimensional graphene-nickel foam-polymer composites (GNPs) and then explored their microstructures and electrochemical responses when both graphene and nickel were exposed to a corrosive solution. It was found that the corrosion resistance of the GNPs decreases with increasing graphene thickness. This is considered to be caused by galvanic corrosion between the graphene and the nickel foam. The findings suggest that the intactness of the graphene film is very important when it is used as a protective barrier for long-term corrosion prevention.