The paper presents the results of investigations of mechanical and thermal properties of poly(ethylene naphthalate) and poly(ethylene terephtalate) blends. The elongation, tensile and impact strength. Brinell hardness and thermal properties has been presented in this paper. It has been observed that thermal resistance of the blends improves with the increase of PEN share in the blends. The mechanical properties show the small increase with increasing the PEN share in the blends, only the elongation of the PEN/PET blends shows a great increase to compare with PET. DSC study show that all blends have double glass transition and melting temperatures and allowed to determine the crystalinity of the blends.