Carbon nanotube (CNT) is increasingly applied as a reinforcement of polymer matrix composite because of extremely high mechanical properties. Among several forms of CNT reinforcement, CNT yarn can be a next-generation reinforcement which enables the use of CNTs in the macro-scale. In this study, untwisted CNT yarns were fabricated by the dry spinning method using a die and graphitized in order to develop CNT yarns with high strength and stiffness. Impure materials and defective structures on MWCNTs were removed after graphitization treatment. G/D ratio was improved more than 10 times. Stress transfer between constituent MWCNTs of CNT yarns became more effectively by removing impure materials. Consequently, macroscopic mechanical properties of CNT yarns were improved by the graphitization treatment in addition to improvement of MWCNT itself.