The melt processing technique was used to elaborate composites made with a polymer matrix [polymethylmethacrylate (PMMA) or polyethylene (PE)] and multiwall carbon nanotubes (MWCNT). Nanotubes were wrapped by amphiphilic block copolymer (PE–co-polyethylene oxide) in aqueous solution to facilitate the dispersion and the handling. Morphology and physical properties (thermal, mechanical, electrical, and rheological) of the resulting composites were investigated. The wrapping of MWCNT allowed a good dispersion of these nanoparticules in the polymer matrices. Physical properties such as thermal degradation, mechanical behavior, and conduction are improved. The use of wrapped MWCNT allows to reduce drastically the melt viscosity of the blends of crystalline PE composites whereas it is almost non efficient for amorphous PMMA ones.