Metal-carbon nano composites are of a great interest as new generation materials with a set of valuable practical properties. The effect of cobalt nanoparticles and multilayer carbon nanotubes stabilized in a polyethylene matrix on the physic mechanical and thermal properties of these nano composites has been studied. An improvement was detected in the strength and deformation parameters, as well as in the thermal-oxidative stability of the obtained nano composites. This can be attributed to the effects of structural and chemical stabilization of the polymer matrix. Small amounts of these nano fillers introduced into the polymer, play the key role as structure-forming agents-artificial nuclei of crystallization, which contributes to the formation of a small-spherolite structure in the polymer, characterized by improved physical, mechanical and thermal properties in the resulting nano composite.