1. The therapeutic effect of organic germanium compound, 2-carboxyethylgermaniumsesquioxide (Ge-132), for experimental osteoporosis was studied using ovariectomized rats maintained on a low calcium containing diet. 2. Serum calcitonin (sCT) level was decreased and serum parathyroid hormone (sPTH) level was increased by ovariectomy and the decrement and increment rates, respectively, were reduced by administration of Ge-132. Thus, the sCT/sPTH ratio was greater in the groups given Ge-132, indicating that the resorption was somehow inhibited by Ge-132. 3. The transverse strength of femur bone was significantly enhanced by Ge-132. 4. A trend was found in the group given Ge-132 for a larger femur cortical bone index. 5. The relative femur bone wet weight was greater in the group given Ge-132. 6. These results indicate that Ge-132 prevents decreased bone strength, and affects the femur cortical bone index, and bone mineral mass caused by osteoporosis.