The intact dental pulps which were free of their tooth bud from adult rat incisors, and oral mucosa were transplanted subcutaneously in homologous rats to study the formation of calcified tissue. The rat were sacrificed after 1,2,3 and 4 weeks following transplantation of dental pulp and oral mucosa. The samples which contained the transplanted and surrounding tissue were fixed in 10% NBF, stained with hematoxylin and eosin, alizarin red S, von Kossa, and alcian blue. Microscopic examinstins revealed as follows: 1. The transplanted oral mucosas were not calcified but tended to form the epithelial cysts. 2. At 1 week after transplantation of dental pulp the calcified structures were appeared at the periphery of the transplantation of dental pulp but weakly reacted to alizarin red S, von Kossa, and alcian blue. 3. At 2 weeks after transplantation of dental pulp the calcified structures began to expand from the periphery to the center of the transplanted dental pulp and occupied the large areas comparatively, and strongly reacted to alizarin red S, and von Kossa stains. 4. At 3 weeks after transplantation of pulp tissue the fibrous components were grown at the periphery of the transplanted pulp tissuesand at 4 weeks a large amount of fibrous tissues were observed. The transplanted pulp tissue tended to form foreign bodies gradually.