Dimethyl 2-methacryloxyethylphosphonate, its monosodium salt, and methyl 2-methacryloyloxyethylphosphonic acid were synthesized, characterized, and grafted onto low-density polyethylene (LDPE) powder under melt-processing conditions in a Rheocord batch mixer (Karlsruhe, Germany). We studied the graft copolymerization onto LDPE in the presence of free-radical initiators, benzoyl peroxide,and dicumyl peroxide, and we performed grafting onto ozone-pretreated LDPE without any free-radical initiator. Effects of reaction time, initiator concentration, and reaction temperature were studied. The possibility of modifying LDPE in the molten state with phosphonated methacrylates was clearly demonstrated. Graft copolymers were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy, and water contact angles.