The synthesis and the application of graft copolymers prepared from ozonized polyethylene (HDPE) are described. The homopolymer was treated with ozone and then copolymerized with monomers, such as methyl methacrylate, hydroxy ethyl methacrylate, glycidyl methacrylate, maleic anhydride, and ethyl acrylate. The products were used as compatibilizers in HDPE/PET [poly(ethylene terephthate)] blends. The mechanical properties and the influence of graft comonomers are described. The copolymers were characterized by the grafting rate and FTIR spectroscopy.