English The effect of a 20 kHz fixed-frequency ultrasonic static mixer on the production of polypropylene and multi-walled carbon nanotube (MWCNT) composites was studied. Ultrasound was applied to the composite melt using an ultrasonic static mixer located at the outlet of a single-screw extruder. The resulting PP/MWCNT composites were characterized by DSC, TGA, SEM, and RAMAN, and their thermal and electrical conductivity, as well as their tensile properties, were determined.