The preventive effect of calcium hydroxide on the disorder of bone metabolism caused by skeletal unloading was investigated. Skeletal unloading was designed using the model of hindlimb hang in rats. Skeletal unloading for 7 d caused a significant decrease of inorganic phosphorus concentration in the serum and of alkaline phosphatase activity and deoxyribonucleic acid (DNA) content in the femoral diaphysis of rats. Oral administration of calcium hydroxide (16 and 24 mg Ca/kg) caused a significant increase in serum inorganic phosphorus concentration and femoral-diaphyseal calcium content and alkaline phosphatase activity of rats with skeletal unloading. Bone DNA content was significantly increased by the dose of 24 mg Ca/kg. These results clearly indicate that skeletal unloading-induced disorder of bone metabolism is partly prevented by oral administration of calcium hydroxide. Calcium ingestion may be useful as a therapeutic tool in the disorder of bone metabolism caused by skeletal unloading.