Previous study has shown that the iliolumbar ligament is important in restraining flexion, extension, and lateral bending of L5 on S1, and its effect on axial rotation was not apparent at 6 N-m of loading. An apparatus was devised to further evaluate its role in relation to the torsional stability of the lumbosacral junction. Torque-rotation characteristics were studied with 24 cadaveric lumbosacral-pelvic specimens. The specimens were divided into three groups. In Group A, the "facet joints," lumbosacral disc and the iliolumbar ligament were all intact. In Group B, the "facet joints" were removed, and in Group C, both the "facets" and the iliolumbar ligament were removed. The results indicated that the ligament was important in maintaining torsional stability of the lumbosacral junction and contributed to 35.2% of the normalized elastic strain energy of the junction.