The author intended to observe the developmental pattern in mandibular bone and condyle following the loss of function of molar with 5 week-old rats by means of removing the crown of molar. The bjects were observed everyweek during six weeks. The results were as follows : 1. Bone apposition was observed at the root apex and interadicular area of alveolar bone. 2. Development of bone substance in mandible tended to increase in the narrow bone trabeculae and fibrous bone substance. 3. Development of condylar head showed little difference from that of control group and development of calcified zone appeared more or less poorly.