Fused filament fabrication (FFF) and Fused deposition modeling (FDM) are among the most common methods of additive manufacturing technology for a variety of industries. However, the extrusion-based process of these technologies has qualified the usable materials to thermoplastics with inherently limited mechanical properties. Augmenting the properties of these materials by blending them with other polymers or their reinforcement with various additives are among the solutions to overcome this issue. This study examines the result of the introduction of Polybutylene Terephthalate (PBT) to acrylonitrile butadiene styrene (ABS), as one of the most common thermoplastics used in FDM/FFF processes, and explores the effects of the incorporation of Multi-Walled Carbon Nanotubes (MWCNT) to ABS/PBT blend with different filler fractions (0.1, 0.3, and 0.5 wt.%) on the mechanical properties of the printed specimens. In order to assess the mechanical behavior of the printed parts, standard melt flow index (MFI), tensile, three-point flexural, and notched impact tests have been performed on the produced parts. The morphological analyses through Scanning Electron Microscopy (SEM) micrographs have been conducted to inspect the distribution of impregnated MWCNTs and the fracture behavior of the specimens. The most satisfactory improvement has been observed in printed parts of the ABS/PBT/CNT nanocomposites containing 0.3 wt.% of MWCNTs.