The purpose of this study was to identify the periodontal regeneration factors in enamel protein shown to induce cementum- and osteo-promotive activities in vivo. The cementum regeneration (CR), a part of periodontal regeneration, was examined by using experimental cavities prepared in a buccal dehiscence dog model. The CR activity was found in the aggregate consisted of sheath proteins along with a small amount of amelogenins separated from newly formed secretory enamel. The sheath proteins were purified to be homogeneous, and examined for the alkaline phosphatase (ALP) inducing activity of human periodontal ligament (HPDL) cells. Application of 17 kDa sheath protein induced ALP activity in HPDL cells. Peptides synthesized from the sheath protein sequence also showed ALP inducing activity. The 17 kDa sheath protein has cell differentiation activity.