Abstract： Objective:To investigate the structural and cellular changes of thoracolumbar vertebral periosteum in an osteoporotic state using osteoporotic sheep and normal sheep models, provide potential key therapeutic targets and theoretical basis for preventing osteoporotic vertebral compression fractures, and identify potential key therapeutic targets for preventing osteoporotic vertebral compression fractures (OVCF).Methods:Eight healthy adult female small-tail Han sheep, randomly assigned to either the osteoporosis group ( n=4) or the control group ( n=4) were used. Osteoporosis was induced in the experimental group through ovariectomy, low-calcium diet, and injections of methylprednisolone. After 4 months, the T 12 vertebrae were extracted. Micro computed tomography was used to analyze the volume, thickness and number of bone trabeculae. HE staining was used to histologically evaluate the periosteal thickness and cell number. Alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) staining was used to evaluate the proportion of osteoblasts and osteoclasts. Results:Compared to the normal group, the osteoporotic sheep exhibited significantly reduced trabecular volume (BV/TV) , thickness (Tb. Th) , and number (Tb. N) [ (22.708±0.973) % vs (35.409±1.254) %, (8.970±0.473) μm vs (10.432±0.392) μm, (0.025±0.000) mm -1 vs (0.035±0.004) mm -1, all P<0.05], along with a notable increase in trabecular separation [Tb. Sp (27.385±0.318) μm vs (21.935±2.101) μm, P<0.05]. Histological evaluation revealed a characteristic fenestrated trabecular structure in hematoxylin-eosin (HE) stained sections. The cambium and fibrous layer of osteoporotic sheep periosteum were thicker, and the number of cambium cells was higher (all P<0.05) . After standardization, tartrate-resistant acid phosphase (TRAP) and alkaline phosphatase (ALP) staining indicated a significant increase in TRAP + osteoclasts in osteoporotic sheep, while ALP staining of the forming and fibrous layers of the periosteum showed no significant difference between the two groups ( P>0.05) . Conclusion:The vertebral periosteum in osteoporotic sheep exhibits significant differences in structure and cellular composition compared to normal sheep, characterized by increased bone resorption activity with comparable bone formation activity. Treatment targeting the periosteum is expected to be a key area in the prevention of osteoporotic vertebral compression fractures.