Thermoplastic polyolefin (TPO) has gained considerable attention because of having a combination of rubbery and thermoplastic properties and ease of production. Their excellent weather resistance, low density, and relatively low cost make them attractive materials for the automotive, electrical, footwear industries and membranes for water treatment. Their main shortcomings are poor mechanical properties, especially at low temperatures because of the opposing trends of stiffness and toughness. In this paper, recycled low density polyethylene (RLDPE) was integrated with ethylene-propylene-diene rubber (EPDM) incorporating very low content of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) to improve the mechanical properties of the produced TPO nanocomposite. TPO has been prepared through the combination of 40, 50, and 60 wt.% RLDPE and 40, 50, and 60 wt.% EBDM. The improved TPO composition was then reinforced with 0.1, 0.3, and 0.5 wt.% MWCNTs-COOH to produce TPO nanocomposites. The compounding of TPO and its nanocomposites was done by melt mixing followed by heat pressing. Mechanical and thermal behaviors of the TPO nanocomposites were investigated. Tensile tests showed that the TOP (60-40) is the best improved concentration; the storage modulus of nanocomposites was enhanced by increasing MWCNTs-COOH concentration. In addition, modulus, stress/strain and toughness of TPO were enhanced by adding 0.5 wt.% MWCNTs-COOH. Thus, MWCNTs-COOH reinforced TPO due to not only its large aspect ratios but also due to its interaction with both the TOP matrix and the combatibilizer. The results of microstructural investigations of the prepared TPO nanocomposite using FTIR and TGA confirmed the interaction between MWCNTs-COOH and TPO matrix