Abstract:[Objective] To observe the histological changes in terms of bone microstructure of the lumbar spine and femur in ovariecto- mized rats. [Methods] A total of 50 12-week-age female SD rats were divided into two groups by random number table method, 25 of them underwent ovariectomy (OVX) , while the remaining 25 animals received sham operation (SO) . At 1, 4, 8, 12 and 16 weeks after operation, 5 animals in each group were sacrificed, and 4 μm sections were made from the L5 vertebral body and the femoral metaphysis with HE stain- ing. The trabecular width, the distance between the trabecular interval and cortical bone thickness were measured by usign NS-Elements D microscopic image processing software. [Results] The width of trabecular bone significantly decreased (P＜0.05) , whereas the distance be- tween trabecular bone significantly increased (P＜0.05) , and the cortical bone thickness remained unchanged in the OVX group over time (P＞ 0.05) . By contrast, the trabecular width, the distance between trabecular and cortical bone thickness remained unchanged in the SO group (P＞0.05) . In term of comparison between two groups, there were no significant differences in the width of bone trabecular and the distance between the two groups at 1-8 weeks after surgery (P＞0.05) , while the OVX group had significantly lower width of trabecular bone, greater distance between trabecular bone than the SO group at 12 and 16 weeks after surgery (P＜0.05) . However, there was no significant difference in cortical bone thickness between the two groups (P＞0.05) . [Conclusion] After ovariectomy, the rat has significantly osteoporotic bone mi- crostructure variations, which in lumbar vertebrae is earlier than that in the femur, and in the trabecular bone earlier than that in cortical bone. The bone morphometry has certain diagnostic significance.