Mechanical and dynamic mechanical properties of a waste rubber powder-filled high-density polyethylene (HDPE) composite are investigated. Rubber powder is surface-modified with acrylamide (AAm) using ultraviolet. Rubber powder and HDPE are extruded using a single-screw extruder and maleic anhydride-grafted polypropylene is added as a compatibilizer to improve the adhesion between rubber powder and HDPE. The tensile stress and strain of AAm-grafted rubber powder/compatibilizer/HDPE composites always exhibit higher values than those of unmodified rubber powder/HDPE composites. Surface modification of rubber powder is shown to decrease the magnitude of the tan delta of the HDPE composite. Higher values of the notched Izod impact strength of a surface-modified rubber-filled composite is observed compared to those of unmodified rubber-filled composite. Experimental results show that acryl amide-graft-cd rubber powder reacts with maleic anhydride and it results in improved mechanical properties of the HDPE composite.