Objective To explore the possible action mechanism of Zuogui Pill（左 归丸） in prevention and treatment of glucocorticoid-induced osteoporosis（GIOP）. Methods A total of 18 SD rats were randomly divided into control group

model group and Zuogui Pill group

with 6 in each group. Rats in the model group and Zuogui Pill group received subcutaneous injection of dexamethasone

0. 6 mg/kg

1 time every 3 days

to establish GIOP rats model. Zuogui Pill group also received intragastrical administration of aqueous extract from Zuogui Pills

1. 9 g/（kg·d）.The control group and model group were given intragastrical administration of normal saline 1 ml/（100 g·d） for continuous 8 weeks. The bone mineral density

biomechanical index and the expression of Runt 2

cathepsin K（CTSK）and mammalian target of rapamycin complex 1（m TORC1） mRNA in lumbar vertebrae were detected. HE staining was used to observe the morphological changes of the lumbar spine. The serum alkaline phosphatase（AKP） activity in rats was detected. Results HE staining showed that the number of bone cells in the trabecular bone of the model group was reduced

and the osteoblasts and osteoclasts on the trabecular bone surface were sparse. Compared with the model group

the number of bone cells in the trabecular bone

osteoblasts and osteoclasts on the trabecular bone surface of the Zuogui Pill group were increased significantly. Compared with the control group

the bone density

bone mineral content

compressive strength

energy absorption

m TORC1 mRNA expression and serum AKP activity of the model group were decreased（P < 0. 05）. The lumbar vertebrae bone density

bone mineral content

compressive strength

m TORC1 mRNA expression and serum AKP activity of Zuogui Pill group were higher than those in the model group（P < 0. 05）. Conclusion Zuogui Pill can improve GIOP

and m TORC1 may be an important target.