A novel technique was developed for direct joining between ethylene propylene rubber and high ductile spheroidal-graphite cast iron using functional polymeric nanofilm without any adhesive. The functional polymeric nanofilm was created on the surface of cast iron by means of polymer plating with a synthesized organic compound of 6-diallylamino-1,3,5-triazine-2,4-dithiol monosodium salt. High peel strength joints of the rubber to polymer-plated cast iron were achieved by adding an accelerating agent of perhexane 3M under crosslinking condition of 418 K for 7 min. As the thickness of polymeric nanofilm was around 8.5 nm, peel strength of the joints was high to 8.9 kN/m and its broken-out section was rubber cohesive failure with 100% rubber coverage. Rubber/cast iron joints possessed good heat-resistant property. The film thickness and perhexane content had large effects on water resistance of joints. It is considered that high joining property results from chemical bond at interface between polymer-plated cast iron and rubber chain.