Modification of multi-walled carbon nanotubes (MWCNTs) by means of imidazolium ionic liquid (IL) was performed. Structural characterization of funtionalized nanofillers (IL-f-MWCNTs) was made by means of Raman spectroscopy and transmission electron microscopy. MWCNTs and IL-f-MWCNTs were introduced within ethylene octane copolymer (EOC) with octene co-monomer content of 17% by using the masterbatch approach. The efficiency of the carbonaceous nanofiller distribution within the polymer matrix was characterized by means of scanning electron microscopy. It was shown that MWCNTs and IL-f-MWCNTs were both effective in rising storage modulus, tensile modulus, stress-at break, and electrical conductivity of EOC-based nanocomposites along with the increasing nanofiller content. Besides, it was observed that the modification efficiency of the investigated EOC matrix composites by IL-f-MWCNTs was greater in comparison to pristine MWCNTs.