In mice ranging in age from birth to 45 weeks, the cartilage plate in the spinal column was systemically examined by light and electron microscopy. In addition, the proximal end of tibia in 3 week-old mice was studied for comparison. In early life immediately after birth, the nucleus pulposus was separated by cartilage tissue from the ossified vertebral body. The cartilage could be divided into two portions, one portion close to the nucleus pulposus and the other close to the vertebral body. At 1 week, the cartilage toward the nucleus was further divided into two layers, a superficial thin cartilaginous layer close to the nucleus and a deep layer composed of degenerating and degenerated chondrocytes and calcified matrix. After 8 weeks, the deep layer was invaded with numerous irregularly-shaped cavities which contained osteoblasts, osteoclasts and blood vessels. Thus, the deep layer could be considered to be ossified. On the other hand, the cartilage which was near the vertebral body in early life, consisted of chondrocytes which were arranged in column. Thus the cartilage near the vertebral body was thought to be involved in ossification and development of the vertebrated body. From a comparison with the proximal end of tibia, the superficial layer close to the nucleus pulposus, the succeeding deep portion, and the cartilage close to the vertebral body seemed to correspond to the articular cartilage, the secondary ossification center, and the epiphyseal plate of long bones, respectively. Thus, the junction of vertebral bodies was thought to be similar in structure to the joint between long bones. Therefore, the cartilage plate of the spinal column can be regarded to belong to a component of the vertebral body.