Ten fresh-frozen cadaveric ankles were studied to investigate the effect of an ankle brace (Air-Stirrup) on the three-dimensional (3-D) motion and contact-pressure distribution of the talo-tibial joint with lateral ligamentous injury. Three-dimensional motion and contact-pressure distribution were simultaneously measured under dynamic conditions employing a direct linear-transformation technique and a dynamic-pressure sensor, respectively. Inversion increased significantly upon severing of the anterior talo-fibular (ATF) ligament and calcaneo-fibular (CF) ligaments; however, restoration to the intact level was observed following application of the ankle brace. Internal rotation also increased upon severing of the lateral ligaments in the plantar flexion; however, this difference was not altered by using the ankle brace. The contact area on the articular surface of the talus shifted from posterior to anterior between plantar flexion and dorsal flexion; additionally, a high pressure area was evident in the medial aspect of the talus following severing of the lateral ligaments. Upon application of the ankle brace, however, no significant changes were apparent in the contact condition. The results of this study suggest that stabilization against inversion is the major function of braces in terms of protection of ankle sprains. Ankle sprains, however, often occur in combinations of inversion, plantar flexion and internal rotation; therefore, restriction of plantar flexion and internal rotation may also be an important function of the ankle brace.