Cheonnyuncho (Opuntia humifusa), rich in polyphenols and flavonoids, is known to have medicinal benefits in the treatment of arteriosclerosis and inflammation. This study was undertaken to evaluate the effects of cheonnyuncho seed powder (OHS) on postmenopausal osteoporosis in ovariectomized rats. OHS treatment prevented an ovariectomy (OVX)-induced decrease in biomechanical quality of femurs. OHS also dose-dependently inhibited bone mineral density (BMD) decreases in femurs, which were accompanied by a significant decrease in skeletal remodeling, as evidenced by decreased levels of the bone turnover markers osteocalcin, alkaline phosphatase (ALP) activity, and serum and urinary Ca excretion. Micro-CT analysis of femoral metaphysics showed that OHS prevented the OVX-induced decrease in bone volume/tissue volume, trabecular thickness, and trabecular number. Concluded, the treatment with OHS improves bone biomechanical quality through modification of BMD and trabecular microarchitecture without hyperplastic effects on the uterus. For these reasons, OHS may be suitable as an alternative treatment of postmenopausal osteoporosis.