Osteoporosis is a common skeletal illness affecting over 200 million people annually with increased prevalence in postmenopausal women. It is associated with reduced skeletal strength and mass, and disrupted microarchitecture. Osteoporotic fractures, especially vertebral and hip fractures, and increased mortality rates are the major health concerns of osteoporosis. Management of osteoporosis can be initiated with lifestyle modifications and vitamin supplements in simple cases. In more aggressive cases, anabolic or antiresorptive agents are employed in order to alleviate osteoporosis and reduce fracture risk. Bisphosphonates are one of the most commonly used medications for management of osteoporosis, but their long-term use is restricted due to their side effects. Hence, there is an urgent need for development of new treatments. Recent studies demonstrated the potential role of phytoestrogens and stem cells to be employed in treatment of osteoporosis. Therefore, the current study was carried out to: 1. Evaluate the efficacy of mesenchymal stem cells (MSCs), bisphosphonates (alendronate) and phytoestrogens (resveratrol) treatment in the ovariectomized rat model of osteoporosis. 2. Investigate the effect of alendronate and resveratrol on MSC therapy in ovariectomy-induced osteoporosis in rats. 3. Understand the underlying mechanisms of action involved in using alendronate, resveratrol and MSCs in treatment of osteoporosis. 4. Explore the relationship between osteogenesis and adipogenesis in ovariectomized osteoporotic rats. To accomplish these aims, 70 female rats were used. The rats were divided into 7 groups (10 rats in each group). Six groups were subjected to bilateral ovariectomy to induce postmenopausal osteoporosis from which, one group served as the untreated ovariectomized control. The remaining group (the Sham group) was subjected to a similar procedure in which the ovaries remained intact. The other groups of ovariectomized rats received the following treatments for 8 weeks: MSCs, alendronate, resveratrol, a combination of MSCs and alendronate, or a combination of MSCs and resveratrol. At the end of the study, blood and bone samples were collected for measurement of factors associated with bone formation and resorption (ALP, PINP, CTX-1, OPG, RANKL, RUNX2) and lipogenesis (PPARɤ). A histological examination was also performed to study the effect of the various treatments on bone structure.