Due to massive development, population explosion, and urbanization, an enormous amount of plastic waste is generated, mainly consisting of bottles made of polyethylene terephthalate (PET). The disposal of these PET bottles is a challenge to society. This paper studied bituminous concrete (BC) mix modified with PET bottles in shredded form with variable size and content by the dry process. The PET content ranged from 3% to 10% of bitumen content and was studied in three sizes (4.75–2.36, 2.36–1.18,
). Performance tests such as Marshall stability, flow value, indirect tensile strength (IDT), and moistness vulnerability of the modified BC mix were performed, and the outcomes were compared with those of untreated bituminous concrete mix without PET. The modified BC mix had a higher resistance to moisture and improved performance against deformation and cracking, because the Marshall stability and IDT improved.