It is well known that the glucocorticoid induces osteoporosis by suppression of the osteoblast, but its effect on the osteoclast hRS some controversy whether it activates or suppresses the osteoclast. If the calcitonin, which is known to suppress the osteoclast, prevents the osteoporosis by glucocorticoid, then the suppression of the osteoclast by the glucocorticoid is not so significant. And if the calcitonin increases the osteoblastic activity, Tc-99m MDP uptake will be increased in spite of the glucocorticoid effect on the osteoblast. The immobilization operation was performed to the right leg of male Wistar rats weighing about 200gm. each. For 16 weeks after operation, rats were injected glucocorticoid alone or glucocorticoid anci calcitonin. The bone density was measured by means of photodensitometry under reference aluminum step wedge and Tc-99m MDP uptake was available to the index of the osteoblastic activity. 1. The bone density of femora! head was markedly reduced than that of femoral shaft following ration of cancellous and cortical components in both site. 2. Glucocorticoid caused decrease in bone density of spine and femur, md there is significantly increase of it when medication of glucocorticoid and calcitonin injection simultaneously than that of glucocorticoid. 3. Tc-99m MDP uptake was revealed significant reduction in medication of glucocorticoid but increase in gi;.:cocorticoid and calcitonin injection simultaneously in later experimental period. 4. There wail, a slight reduction in plasma osteocalcin in medication of glucocorticoid through experimental periods and an increase in its value in case of giving glucocorticoid and calcitonin simultaneously in later experimental period. From these results, we suggest that osteoporosis by immobilization is more pronounced by glucocorticoid hormone and osteoporosis induced by immobilization and glucocorticoid use is prevented by calcitonin administration with increasing osteoblastic activity.