【Abstract】 Objective To investigate the anti-inflammatory effect of Helleborus thibetanus Franchon on collagen induced arthritis (CIA) model rats and the effect on OPG/RANK/RANKL signaling pathway. METHODS Sixty female wistar rats were divided into (1) normal group (Control), (2) model group (Model), (3) positive drug group (methotrexate, MTX), (4) low-dose group, (5) medium-dose group, and (6) high-dose group. The CIA rat model was established by injecting bovine type II collagen into the tail root of rats using the collagen antibody induction method, and the drugs were administered by gavage after the model was successfully established. Normal group: 10 mL/(kg·d) of saline was given; model group: 10 mL/(kg·d) of saline was given; the positive drug group was given 2.0 mg/(kg·d) of MTX each time, three times a week; the iron chopsticks low, medium, and high dose groups were given 0.25g, 0.5g, 1.0g/(kg·d) each time; continuous gavage treatment for 25 day. Body mass of rats was recorded to observe the degree of foot swelling;rat ankle arthritis index score;micro-CT observation of histopathologic changes in ankle joint bone; hematoxylin-eosin (HE) staining for pathological changes in ankle joint bone tissue and synovial membrane of the rats;tests to observe changes in the number of osteoclasts were performed with anti-tartaric acid phosphatase (TRAP) ; PCR to detect the mRNA levels of osteoprotegerin (OPG), nuclear factor-κB receptor activator (RANK), RANK ligand (RANKL), tumor necrosis factor (TNF-α), and bone-forming protein 2 (BMP-2);Relative expression of OPG, RANK, RANKL, TNF-α and BMP-2 proteins were detected by protein immunoblotting (Western blot)Helleborus thibetanus Franchon on rats with rheumatoid arthritis and its potential pharmacological mechanism for osteoarthritic protection. Results The statistical results of the data showed that compared with the normal group, CIA rats showed slower growth of body mass (P<0.05), increased thickness of the plantar foot (P<0.05), narrowing of the joint cavity in the ankle joint, gnawing-like bone destruction of the bone tissues, and pathologic changes in the synovium,Such as inflammatory cell proliferation and abnormal synovial hyperplasia infiltration; Micro-CT results showed that: compared with the normal group, the model group, low and medium dose group, the ankle joint surface was uneven, incomplete in shape, and the ankle joint surface showed gnawing-like bone destruction, and the high-dose group had no significant changes in all indexes compared with the normal group; HE staining found that the ankle joint of the model group showed joint cavity narrowing, gnawing-like bone destruction, synovial tissue proliferation and inflammatory cell infiltration. The pathological changes such as destruction of bone tissue, synovial tissue hyperplasia and inflammatory cell infiltration were found in the ankle joint of rats in the model group; compared with the model group, bone tissue hyperplasia and inflammatory infiltration in the ankle joint of rats in the low, medium and high dose groups were significantly improved; TRAP staining observed that compared with the normal group, the model group had the largest number of osteoclasts, and the number of TRAP staining positive osteoclasts was reduced under the intervention of the low, medium and high dose groups; the results of qRT-PCR showed that, compared with the model group. The relative expression of OPG, BMP-2 mRNA was increased in the low, medium and high dose groups (P<0.05), and the relative expression of RANK, RANKL, and TNF-α mRNA was decreased in the low, medium, and high dose groups (P<0.05); the results of WB, compared with the model group, the relative expression of OPG, BMP-2 protein was increased in the low, medium, and high dose groups (P<0.05), and the relative expression of RANK, RANKL , and TNF-α protein relative expression decreased (P<0.05). Conclusion Helleborus thibetanus Franchon may alleviate the inflammatory response in vivo in RA rats by regulating the OPG/RANK/RANKL signaling pathway and exert its role as an anti-rheumatoid arthritis mechanism.