The preventive and therapeutic effects of aqueous extracts of Mornidae Radix (MR) were observed in sciatic neurectomized mice, a disused osteoporotic model. The right hind limbs of 80 mice were neurectomized and 20 mice were sham-operated and served as a sham control. Then 50, 100 and 200 mg/kg of MR extracts were dosed 3 days after neurectomy for 6 weeks in the prevention study and were dosed 2 weeks after neurectomy for 12 weeks for the therapeutic study. After dosing with the MR extracts, the thickness of the hind limbs, tibia failure load, tibia bone mineral density (BMD), serum osteocalcin levels, tibia calcium (Ca) and phosphorus (P) contents were monitored with histomorphometrical changes of the tibia. In both the prevention and therapeutic studies, the MR extracts significantly and dose-dependently suppressed the decrease in hind limb thickness, tibia failure load, BMD, tibia Ca and P contents with an increase in serum osteoclacin levels. In addition, the MR extracts also significantly and dose-dependently suppressed the decrease in histomorphometrical parameters of the tibia such as volume, length and thickness of trabecular bone and thickness of cortical bone with an increase in osteoclast cells in both the prevention and therapeutic studies. Based on these results, the MR extracts may act as both a suppressor of bone resorption and an enhancer of bone formation in vivo and may have some favorable effects for preventing and treating the osteoporosis induced by sciatic neurectomy.