Abstarct: Reinforcing concrete with steel fiber has been proven being able to improve the properties of concrete such as strain capacity, impact resistance, energy absorption and tensile strength because the discrete steel fibers act as dispersed reinforcement in mitigating crack propagation. Therefore, this study, as part of ongoing research, develops a slip-hardening steel fiber in concrete. For this work, the twisting of two round steel wires each other was adopted with high tensile strength and different number of twisting rounds. There is very limited study on the pullout behavior of twisted steel fibers in technical literature.Therefore, an experimental study was performed to evaluate the pullout behavior of twin-twisted steel fibers and to characterize its tensile performance. Parameters investigated are the number of twist, the fiber embedded length, the compressive strength of the matrix (47, 79, 109 MPa) and the fiber diameter. In addition, steel fiber with hooked ends were also prepared and tested for comparison. The test results quantify the effects of friction bonding and mechanical untwisting on the pseudo-plastic, slip-hardening pullout response of a steel fiber. According to the results, with the increase of the number of twisting of the fibers per unit length, the maximum force of pullout increases. But this increase can cause damage to the matrix tunnel. which adversely influences the dissipate energy during pullout. Also, the tensile stress created in twin-twisted steel fibers and hooked end fibers increases with increasing matrix strength, embedded length and aspect ratio, but this can lead to premature fiber breakage. By comparing the pullout behavior twin-twisted steel fibers and hooked fibers with each other, it can be seen that the new fibers show a better slip hardening characteristics, In such a way that in the pullout energy of twisted steel fibers, almost 90% improvement can be achieved compared to hooked steel fibers.