DM is a systemic disease with many complications. One of them, diabetic osteopenia is important sequelae and many authors reported reduced bone mass in diabetic rats. However, in mandible, study has been rare because of its anatomical limits. So the objective of this study was to investigate bony change in mandible of diabetic rats. Thirty-two adult rats were used in this study. Half of them were male and female respectively. In sixteen rats, streptozotocin was injected intraperitoneally to induce DM and the serum glucose concentration was checked to ensure the induction of DM prior to the time of sacrifice. At 1, 2, 3, 4, 6, 8, 12, 16weeks, control group and diabetic group rats were sacrificed respectively. And then bone mineral density of mandibles and femurs of the rats was measured using dual energy X-ray absorptiometry(DEXA). In addition serum osteocalcin and urine deoxypyridinoline were measured as markers of bone formation and resoption respectively. Mandibular and femoral bone density in streptozotocin induced rats was decreased with significance statistically after 4 weeks from injection. In mandible, comparing with femur, bone density was moderately decreased. The alveolar bone in mandible was more decreased bone density than the whole body in the mandible From these results, bone mineral density decreased in uncontrolled diabetic group with time, and especially alveolar bone was more destructive in the mandible. So authors think that consideration of reduced bone mineral density is necessary in dental procedure.