The work is dedicated to the solution of an important task - the creation and study of new polymer compositions, which, unlike traditional polymeric materials, are characterized by polyfunctionality and high performance characteristics.Over the past few decades, among nanofillers, considerable attention has been paid to carbon nanotubes (CNTs) due to their special mechanical and thermal properties, geometric parameters, low mass density and their inherent electrical properties. As a polymer matrix for studying systems with an active interaction of components, it is proposed to use polymers that are capable of crystallization and include polar groups. A typical representative of such polymers is the high molecular weight polyester - penton. Such composite systems are favorably distinguished by the presence of two phase instabilities in the temperature range under study, namely, the melting of the crystalline phase and the glass transition of the amorphous component of the polymer matrix, which will provide more complete and deeper information about the mutual influence of the components of such systems. The ultrasonic method has been used for experimental study of the acoustic properties and structure of polymer nanocomposites of the penton - carbon nanotubes system. An analysis of the studied concentration dependences of the characteristics at frequencies of 5, 7.5, and 10 MHz indicates a strong character of the interaction between the penton - CNT system components. The research results indicate that the ultrasound velocity in filled systems in the entire studied concentration region is significantly higher than for an unfilled penton, and for thecarbon nanotubesfilled penton, a significant increase in the elasticity of the composite compared with an unfilled polymer matrix takes place. Obviously, this can occur due to a significant change in the structure of the polymer component of the system and the formation of an interfacial layer around the CNT with a more ordered structure respectively to pure penton. Additional information is provided by the dependences of the “jump” of the absorption coefficient on the frequency and the dependences of the tangent of the angle of mechanical losses (tgδ), which indicate that the size of carbon nanotube aggregates in the penton matrix as an obstacle to a mechanical wave is much smaller than the size of the penton particles, and the constancy of all studied characteristics when the concentration of CNTs φ ≈ 0.3 vol. % indicates the transition of the penton at this concentration to the state of the wall layer.