Additive manufacturing, commonly known as 3D printing, first emerged in the 1980s. Currently, the application of 3D printing has been expanded to various areas, such as automotive, aerospace and bio-engineering to mention a few. However, a number of serious challenges with the 3D printing fabrication have been found such as lower mechanical characteristics, relatively high surface roughness and anisotropy in mechanical and physical properties. To expand 3D printing technology into practical final products manufacturing, the improvement of the mechanical properties for the 3D printed parts should be addressed. To this end, the work reported in this thesis is focusing on searching for feasible approaches to improve the mechanical behavior of the 3D printed mono-component and bi-component polymer objects. Specifically, the heat treatment was conducted to improve properties of mono-component samples fabricated from poly (lactic acid) (PLA) and polyethylene terephthalate glycol modified (PETG) filaments. Then, PLA/PETG bi-component hybrid structures were fabricated and heat treated to improve their mechanical characteristics. Further improvement of the mechanical properties for the printed bi-component structures was achieved by utilizing PLA/PETG blend filament. At each step, the morphology, structure, and properties of the materials used and printed samples were characterized using optical microscopy, rheometry, atomic force microscopy, thermal gravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, tensile tests and dynamic mechanical analysis (DMA).