There is an increasing demand for carbon fibers (CFs) that are affordable and have outstanding mechanical properties in a wide range of industries. Asphaltenes (i.e., the heavy fraction of bitumen) have recently been identified as promising low-cost precursors for developing low-cost carbon fibers that could accelerate the widespread adoption of CFs in existing and new industries. The thesis was initiated by exploring the utilization and effectiveness of asphaltene-derived carbon fibers (ACFs) in carbon fiber-reinforced composites (CFRCs) produced through additive manufacturing. Leveraging the high aromaticity and carbon content of petroleum asphaltenes, ACFs offer a cost-effective alternative to commercial carbon fibers (CCFs) derived from polyacrylonitrile (PAN). Composites were 3D printed by incorporating different weight proportions (0%, 2.5%, 5% and 7.5%) of chopped ACFs (length 3-4 mm, diameter ~6-12 μm, tensile strength ~500-1150 MPa, tensile modulus ~40-90 GPa) into an acrylonitrile butadiene styrene (ABS) matrix without any post-treatment. Mechanical properties of both ACFs and their derived composites were extensively characterized, including tensile, flexural, hardness and impact properties. Results indicate that incorporating 7.5 wt% ACFs enhanced ABS's flexural and tensile strengths by approximately 20% and 5%, respectively and its corresponding modulus values by about 30% and 34%. Additionally, ABS's hardness improved by 31% with the inclusion of 7.5 wt% ACFs. Despite the lower surface roughness and surface energy of untreated ACFs, the composites exhibited promising performance. To address the poor interfacial adhesion between the hydrophobic, chemically inert ACFs and the polymer matrix, various surface treatments (HNO3, silane, H2O2, etc.) were proposed to introduce polar functional groups and increase surface roughness. Furthermore, the ABS matrix was grafted with maleic anhydride (MA) to facilitate better bonding with surface-functionalized ACFs. This study systematically investigates the effects of these surface modifications on the properties of ACFs and the fiber-matrix interface, demonstrating that surface treatments can significantly enhance the fiber-matrix compatibility of ACF-reinforced composites, making them viable for a wide range of applications.