Abstracts: The present study was carried out to investigate the morphological changes in the alveolar bone in rats fed a low calcium diet, in order to establish an experimental model of alveolar bone resorption. Male Wistar rats (70-85g in body weight) were either fed a low calcium diet (0.05% Ca, 0.35% P) or a control diet (0.5% Ca, 0.35% P) by using a pair feeding technique. The rats were sacrificed at intervals of 3, 6, 9 and 20 days. No difference was found in the growth rate between the control and the low calcium group. In the low calcium group, the bone area significantly reduced at day 3 and progressively decreased to 46% of that of the controls by the end of the experiment. The bone resorption was obvious in the cancellous bone during the early period of the experiment and then the cortical bone was seen to resorb. However, the contour of bone and the rate of bone apposition did not change. At day 20, bone still remained in three regions: the alveolar bone proper that surrounds the tooth sockets, a few cancellous bones and a thin wall-like cortical bone. These results suggest that the process of alveolar bone resorption is related to the mechanical forces induced by the occlusal function of the tooth and, further, that this experimental model might be useful for investigating the mechanism of alveolar bone resorption and disorders of the alveolar bone.