Nowadays the application of polymer composites is increasing, because focused choice of components and their weight ratio allows creating materials with unique properties spectrum, which is not characteristic for the chosen components separately. In the current research we study popular engineering polymer, polyoxymethylene (POM), compositions with different thermoplastic elastomers, ethylene octene copolymers (EOCs), with varying octene content (17% and 38%). POM/EOC17 and POM/EOC38 compositions at broad wt.-to-wt. ratios (10, 30,50,70,90 POM wt. %) were obtained by using twin-screw extruder. Some structural and mechanical properties of all the selected composites were investigated. POM/EOC17 and POM/EOC38 structural properties were investigated by using differential scanning calorimetry (DSC) and density analysis. It is demonstrated that by increasing the content of one of the blend’s components crystallization of the other’s is affected. As follows, components hinder each other’s crystallization, especially in the case of POM/EOC17. By the differences between the values of experimental and additive densities, it is concluded that composition POM/EOC17 possesses somewhat lower void content. Considering that the difference between the melting temperatures of the component crystalline phases is smaller for POM blend with EOC17, it could be assumed that possibility of the occurrence of thermooxidative processes in POM/EOC17 compositions is somewhat lower; thus smaller is the possibility for voids and structural defects to develop in these compositions