Calcium deficiency causes mobilization of calcium from bone and leads sooner or later to osteoporosis, that is to say a reduction in the amount of calcium in bone or decrease of apparent bone density. Recent studies showed that isoflavones prevent bone loss associated with ovarian hormone deficiency in women and animal models. This protective effect of isoflavones may be partly due to its estrogen-like ability regulating calcium absorption and bone metabolism. This paper reviewed the recent reports of such studies.