Polymer nanocomposites are in the focus of global academic research of recent years due to enormous possibilities to obtain unique original materials with substantially improved exploitation properties, necessary for applications in energetics, electrotechnics, electronics, structural engineering and other relevant fields of national economy [1-5]. Unique properties of the nanocomposites are generally imparted by modifying the matrix polymer by addition of nanostructured fillers of various geometries. Carbon allotropes, among them fullerenes, nanotubes and graphene, represent the most versatile class of nanostructured fillers. Introduction of carbon allotropes within polymer matrix is burdened due to the absence of functional groups on the surface of the nanofiller. Consequently, successful introduction of carbon nanofillers within polymer matrix requires some surface modification of the nanofiller, in spite of the fact that this can lead to certain impairment of it unique electrical, thermal and mechanical properties. Functionalization of carbon allotropes with carboxyl, hydroxyl, acyl, amine and amide functional groups are most widely known [6-8]. The current research considers modification of thermoplastic polyolefines and polyolefine copolymers by means of functionalized multi-walled carbon nanotubes (MW-CNTs). Covalent and non-covalent functionalization routes (including carboxylation and treatment with ionic liquids) of MW-CNTs have been considered. The amount of neat and functionalized MW-CNTs in a polymer matrix has been changed in a rather broad range from 0,5 to 10,0 wt.%. The effectiveness of direct melting and masterbatch approaches has been compared for obtaining the nanocomposites with desirable dispersion of the nanofillers within the thermoplastic polyolefine matrix. MWCNTs dispersion patterns within the polymer matrix have been studied by means electron microscopy. Electric and mechanical performance of the nanocomposites has been characterized by means of broadband dielectric spectroscopy as well as dynamic mechanical thermal analysis. The factors of external environment (UV irradiation, temperature, moisture content) on the electrical and mechanical properties of the aforementioned polymer nanocomposites have been also evaluated. Especial attention has been paid to evaluation of reinforcing efficiency of MW-CNTs on the accelerated weathering impaired polymer nanocomposites, the aspect investigated relatively scarcely in the scientific literature. Results of the investigation testify that proper choice of the manufacturing technology allows considerably improve distribution of the nanofiller within the thermoplastic polymer matrix. Besides it has been observed that by increasing the nanofiller content within the polymer matrix elastic and dielectric properties of the investigated nanocomposites can be considerably increased. Especially remarkable is protective role of MWCNTs on the properties of UV impaired polymer nanocomposites.