The effects of carbon nanotubes (CNT) functionalization by plasma on morphology and thermo-mechanical properties of polyamide 6 (PA6) and polypropylene (PP) blend were investigated. CNT functionalization was carried out with radio frequency plasma in different methods: Ar/O2 gas mixture and using maleic anhydride (MA) by its insertion in the solid form through a mixture with CNT. Nanocomposites containing pristine, oxidized and maleic anhydride functionalized MWCNT with 0.5 wt% were prepared by melt mixing using a torque rheometer. The functionalized CNT was characterized by X-ray Photoelectron Spectroscopy (XPS). The CNT treated by Ar/O2 gas mixture present higher oxygen concentration than that treated by maleic anhydride. Nanocomposites with functionalized CNT showed better nanoparticles dispersion and distribution. Despite the higher oxygen content on CNT functionalized by Ar/O2, an adhesion improvement between the phases and morphological stability were observed with the addition of CNT functionalized with maleic anhydride. Also, an increase of 26% in storage modulus was observed for PA6/PP nanocomposites with CNT functionalized with maleic anhydride.