Osteoprotegerin (OPG) and receptor activator of nuclear factor-kappa B ligand (RANKL) have been revealed in the pathogenesis of primary osteoporosis and other metabolic bone diseases. This study was designed to assess the effect of 17-β estradiol (E2) treatment and angiotensin converting enzyme inhibitor (ACEI), captopril, on osteoporosis induced by ovariectomy in rats and discussing the role of OPG/RANKL ratio in their action. Thirty two adult female rats were divided into four equal groups. Group I: control group, Group II: ovariectomized (OVX) non treated group, Group III: OVX rats treated with E2, Group IV: OVX rats treated with captopril. OVX rats showed a significant decrease in serum Ca2+ and OPG levels with significant increase in serum RANKL, osteocalcin, alkaline phosphatase activity and urinary hydroxyproline levels. Treatment with captopril as well as E2 led to a significant improvement in bone markers levels with a significant increase in OPG/RANKL ratio. Image analysis technique revealed that there was a significant improvement in cortical bone thickness (CBT) and mean trabecular bone density (TBD) in OVX rats treated with either E2 or ACEI. So, we can conclude that the protective