Modification of multi-walled carbon nanotubes (MWCNTs) with ionic liquids has been performed. The method has been developed to improve dispersion of MWCNTs within polymer matrix. The influence of unmodified and modified MWCNTs on the structure, as well as electrical, elastic, micromechanical and thermal properties of ethylene-octene copolymer (EOC) composites has been evaluated. Concentration of MWCNTs in the polymer matrix has been changed within a broad range from 0,5 to 15 wt.%. It has been concluded that quasistatic and dynamic modules of elasticity, ultimate tensile stresses and strains, as well as microhardness increase due to the introduction of carbon nanofiller within the polymer matrix. Simultaneously electrical conductivity of the EOC matrix composites is increased. In general, one can conclude that by introduction of modified MWCNTs in the EOC matrix improvement of exploitation properties is greater than in the case of neat carbon nanofiller modified systems.