Synthetic fiber ropes are widely used for robots because of their advantages such as lightweight, high tensile strength and flexibility. However, there is limited information on the physical properties of synthetic fiber ropes when used for robots. This study focuses on repetitive twisting of synthetic fiber ropes and provides information for selecting them for robots based on durability. To this end, we conducted repetitive twisting experiments on five types of ropes made from different fibers; we revealed that Dyneema has higher durability against repetitive twisting than the other ropes when a single rope is twisted. In addition, we conducted experiments on Dyneema by applying torsion to two ropes in parallel like a twisted string actuator. The result indicated that two Dyneema ropes in parallel have higher durability than a single rope; however, we revealed that the the tensile strength decreases sharply with an increase in the angle of twist.