Additive manufacturing (AM) enables cost effective production of complex shapes with providing design freedom. Fused deposition modeling (FDM) has been one of the most ac- cessible AM methods which guide thermoplastic filaments to provide accurate and easy pro- duction of 3D objects layer by layer fusion. However, this technique has brought some draw- backs associated with limited material choices including relatively weak structural properties, low resolution range, and restrained processability in 3D printers. To overcome these flaws of FDM, herein we described the fabrication of high-performance thermoplastic fila- ments as an FDM feedstock as a stronger replacement of commodity thermoplastics. For further improvement, carbon nanotubes (CNTs) were incorporated into high performance matrices to provide multifunctionality both by improving mechanical properties and elec- trical conductivity. To achieve that, composite polyetherimide (PEI) filaments with vari- ous CNTs fractions were processed by melt compounding without any solvents or additives. Manufacturing process adopted a sequence of twin and single screw extrusion. Thermal transition and rheological changes due to CNTs incorporation were monitored and morphol- ogy, tensile behavior and electrical conductivity of neat PEI and nanocomposite filaments were investigated. The results showed that 5 wt % CNTs reinforced PEI filaments exhibited 55 % higher stiffness compared to neat PEI feedstock. Structural analysis supported that these nanofillers were well dispersed in mix state and electrical percolation threshold of CNTs/PEI nanocomposite filaments was found as low as ca. 0.1 wt % CNTs.