Results concerning the influence of the modification of morphological and chemical characteristics of ground tyre rubber (GTR) powders on the mechanical properties of polyethylene (HDPE or LDPE)/GTR blends are given. In order to improve the interfacial adhesion between rubber particles and matrix, two oxidation treatments of the GTR powder by potassium permanganate (in solution) and γ-irradiation (in air) were performed. Then, the powder was incorporated in a HDPE matrix containing a small amount of maleic anhydride grafted polyethylene (MAgPE). The effect on the mechanical properties of the blends was studied. Since none of them was really effective, we conclude that oxidation cannot compensate for the lack of chemical reactivity of GTR powders.