The tension stiffening index is a critical factor which improved their effect on the torsional behavior of fibrous reinforced concrete beams which included the bond strength between the reinforcement and the concrete, and the amount of reinforcement indexes. Thus, this paper highlights the effect of the tension stiffening index on the torsional resistance of ultra-high performance fiber reinforced concrete (UHPFRC) beams under pure torsion. Therefore, four under-reinforced ultra-high performance fiber reinforced concrete beams were cast and tested under pure torsion which contains the fixed amount of longitudinal and transverse reinforcements, while the grade and the rib pattern on the surface of reinforcement have been changed. Test results verified that the torsional resistance, stiffness of the cracked section and the twisting angle were improved at the crack and peak loads due to a reduction in the tension stiffening index. However, the axial strains in transverse and longitudinal reinforcements.