Runx2 and Osterix, the transcription factors for osteoblastdifferentiation, are known as fundamental factors to regulatethe development of calcified tissues. However, the biologicalfunctions of these factors in the development of the periodontaltissues remain unclear. In this study, we investigatedthe distribution of Runx2 and Osterix during periodontaltissue development of the mice. Mandibles from 14-day-oldmice were prepared for paraffin section. Serial sections of themandible containing 1stmolar tooth germs were obtained as athickness of 7 μm. Some sections were stained with hematoxylinand eosin. Others were used for immunohistochemistry forPCNA, Runx2, and Osterix. Epithelial cells in growing end ofHertwig’s epithelial root sheath (HERS) and mesenchymalcells adjacent to the growing end of HERS expressed PCNA.Undifferentiated mesenchymal cells and hard tissue formingcells like cementoblasts and osteoblasts in early stage of differentiationexpressed Runx2. Fully differentiated cementoblastsand osteoblasts secreting matrix proteins expressed Osterix.However, the cells terminated the matrix formation did notexpress Osterix. Periodontal ligament cells expressed Runx2and Osterix. Pulp cells expressed Runx2 only.These resultssuggest that Runx2 and Osterix might regulate the differentiationof cementoblasts in the same manner as osteoblasts.Runx2 might participate in the process of cementoblastdifferentiation in early stage, whether Osterix might regulatethe maturation and matrix synthesis of the cells.