Polyethylene terephtalate (PET)/linear low density polyethylene (LLDPE) blends compatibilized with diethylmaleate grafted polyethylene (DEM-g-LLDPE) were characterized by FTIR spectroscopy, thermogravimetrical analysis (TGA) and scanning electron microscopy (SEM). FTIR and TGA results indicate that there are interactions between the components of the blends, which produced variations in the infrared bands associated with the conformational changes (from gauche to trans) within the glycolic sequences of the polyester and a sinergistic effect on the thermal-oxidative stability of the compatibilized blends. Morphological analysis showed a dispersed particle size reduction and a better adhesion between the matrix and the disperse phase.