In order to determine effects of atlas burst fracture on the stability of the occipito-at-lanto-axial complex, six fresh bony and ligamental cadervic specimens of occipito (C0) to (C3) were used to produce atlas burst fracture model by osteotomy. 1.53Nm pure moment was applied to the complex to produce its physiological three-dimensional motions.this ex-perimental result suggested that atlas burst fracture severely affects the stability of the occi-pito-atlas-axial complex, but does not cause its axial rotational instability. If atlas burst frac-ture is associated with transverse ligament rupture, the stability of the occipito-atlas-axial complex increases more than the former and its axial rotational is also lost. Therefore, the status of transverse ligament is the most important indicator for evaluation the acute instabi-lity of the occipito-atlanto-axial complex caused by atlas burst fracture. The biomechanical basis for surgical and non-surgical treatment for atlas burst fracture is also discussed.