Abstract <p>The effect of nanofiller additives containing cobalt oxide nanoparticles stabilized by a polymer matrix of high-pressure polyethylene, obtained by a mechano-chemical method, on the structural features and properties of metal-containing nanocomposites based on isotactic polypropylene (PP) and high-pressure polyethylene (PE) was studied using differential thermal analysis, X-ray diffraction, and scanning electron microscopy analysis. An improvement in the strength, deformation and thermal-oxidative stability of the obtained nanocomposites was revealed, which is apparently due to the synergistic effect of the interphase interaction of cobalt-containing nanoparticles in the PE matrix with the components of the PP/PE polymer composition.</p>