The results of study on stress distribution of the lumbar spine analyzed with a mechanical model of the lumbar motion segment constructed by a three-dimensional finite element method, and the comparison of resulting values with the corresponding bone density represented by the attenuation value of CT were reported. The results indicated that the stress levels in various parts of the lumbar spine were closely related to the CT values. The authors conclude that the mechanical stress is an important factor in maintaining the dynamic balance of bone growth.