It is of a great challenge to apply nonmetal fractions (NMFs) of waste printed circuit boards (WPCBs) as reinforcing fillers in rubbers. In this paper, a typical amorphous synthetic rubber, ethylene propylene terpolymer (EPDM), is used as the model material to investigate the mechanical properties of EPDM/NMFs composites. A multifunctional grafting monomer containing two thiol groups and two carboxyl groups is designed and synthesized. The monomer is used to synthesize highly grafted EPDM-g-AA via melt grafting. Tensile strength of EPDM/NMFs composite sharply increases to 18 MPa when 10phr of EPDM-g-AA is used. The grafted polymer also significantly improves the thermal oxidation resistance. It can be expected that the strategy is able to be expanded to other rubber systems and opens the door to application of NMFs in rubber industry.