The evaluation of torsion investigations is based on the increasing demand for the creative design of curved structural members; yet, they are limited concerning lightweight concrete beams. Lightweight concrete has many and diverse utilizations, including multistory building frames and floors, curtain walls and bridges. This paper investigated the effect of fiber on torsional behavior of lightweight concrete beam. Many variables were studied such as compressive strength of lightweight concrete, fiber type, fiber volume ratio, spacing between stirrups, diameter of stirrups and CFRP reinforcement. The numerical results showed that the increment in fiber content resulted in better mechanical properties and torsional resistance of lightweight concrete beams. The effect of carbon fiber and steel fiber is evident from the volume ratio 2%, which produced the highest ultimate torque enhancement to 77.64% and 76 % respectively. In addition, a rational approach is proposed to predict ultimate torque to develop the torsion design of lightweight concrete beams.