Sensors, actuators and other smart devices require use of advanced materials demonstrating change of certain physical properties under the influence of external fields, such as electromegnetic field. Response behaviour of so called smart materials may be improved by hybridization. For an example, by modifying a polymer matrix with nanofillers of different aspect ratios or chemical functionalities may endow unique set of properties to the resulting composite thus enhancing its application potential. Thus co-synthesyzed hybrid fillers from carbon nanotubes (MWCNTs) and iron(II, III) oxide (Fe3O4) may be used to tailor electrical and magnetic properties to a polymer composite. The current research is devoted to development and characterization of smart ethylene-octene (EOC) nanocomposites with magnetite (Fe3O4), multi-wall carbon nanotube (MWCNT) and MWCNT/Fe3O4 hybrid fillers. In the first stage of the research a method of functionalization of multi-wall carbon nanotubes (MWCNT) with magnetite (Fe3O4) has been acquired to obtain MWCNT- Fe3O4 hybrids at different proportionality ratios of the ingredients. In the second stage of the research a method of development of the hybrid filler modified ethylene-octene copolymer (EOC) masterbatches is used to obtain thermoplastic EOCMWCNT/Fe3O4 composites. Structural, mechanical, thermal, electrical and magnetic properties of the obtained hybrid nanocomposites have been characterized. It has been revealed that the highest stiffness, thermal stability and electrical conductivity of the nanocomposites may be achieved by introducing MWCNT containing nanofillers in the EOC matrix. However, by increasing Fe3O4 content in the hybrid nanofiller leads to improved thermal conductivity and magnetic properties of the investigated nanocomposite. Use of MWCNT/30Fe3O4 hybrid filler ensures considerable increment of EOC nanocomposite’s electrical conductivity and moderate increment of its thermal conductivity, which is important for development of innovative thermoelectric devices [1].