•The use of synthetic fiber-enhanced mechanical properties on torsional hollow beams.•The enhancement in beam performance was relative to the fiber type and length.•The torsional ACI equation was modified to incorporate the synthetic fiber effect. Past research has used synthetic fiber (SY.F) and steel fiber (ST.F) for decades to advance concrete mechanical characteristics, including shear, tensile, and flexural strengths. Nevertheless, there is limited information concerning the torsional concrete reinforced with SY.F and ST.F performance. This research aims to explore the torsional performance of hollow reinforcement concrete beams reinforced with various fiber types. The fiber content of 1% with three different lengths of SY.F, 19, 38, and 57 mm, along with 13 mm of ST.F, was used. Two specimens were cast with normal concrete without using fibers as control beams and four hollow beams with ST.F and SY.F. To use a pure torsional load on the tested samples, an innovative test method was employed. The twisting angle of tested beams was calculated at each interval of the load as well as the first crack load and failure load. Outcomes illustrated that the utilizing of SY.F and ST.F in the reinforced concrete beams (RCB) enhanced the overall performance under torsional load compared to the control beam behaviors. This enhancement in the performance was relative to the fiber type and length. For the first cracking load, the tested beams reinforced with the ST.F and SY.F of 19 and 37 mm lengths showed approximately the same value. Also, the beam reinforced with the SY.F length of 55 mm exhibited the highest first cracking load value, among other tested beams. As the fiber length increases of SY.F, the ultimate load capacity was raised by 4.7, 9.4, and 21.9% for beams cast with 19, 37, and 55 mm fiber length, respectively. For the ST.F reinforcement concrete beam, the ultimate load capacity was raised by 5.5%. Therefore, due to the significant impact of SY.F on the torsional performance, it is recommended using SY.F with normal concrete.