In this article, the effects of the grafting degree and the processing conditions employed to prepare LLDPEs-g-DEM and HDPEs-g-DEM via reactive extrusion on their rheological and thermal properties were studied. The rheological properties of the virgin samples of LLDPEs, HDPEs, and their functionalized products were determined using capillary and dynamic rheometry. The thermal behavior of the virgin materials and their grafted products was examined by differential scanning calorimetry (DSC). It was found that the rheological properties are more sensitive than are the molecular structure characteristics to the changes produced by the grafting reactions with DEM, under the employed experimental conditions. There is an increase in the dynamic viscosity at low frequencies, in the storage modulus, and in the shear-thinning behavior when the grafting degree increases. The crossover between G " and G＇ moves to lower frequencies and the relaxation time spectrum functions are broader in the grafted materials.