The effects of high-density polyethylene (HDPE) and crumb rubber powder (CRP) on the properties of hot mix asphalt were investigated. The physical properties, penetration, softening points, and ductility of unmodified and modified asphalt were measured for various HDPE and CRP contents. Marshall stability and flow, Marshall quotient, moisture sensitivity, and wheel tracking (rutting) tests were also conducted. The results showed that using HDPE and CRP as modifiers improves the physical properties of asphalt and Marshall properties of HMA mixtures. The resistance to moisture damage increased significantly after the addition of HDPE and CRP, as did the resistance to permanent deformation.