OBJECTIVE： To study the effects of Alangium chinense water extract on the levels of IL-1β and TNF-α in serum and OPG/RANKL/RANK system in synovium of type Ⅱ collagen-induced arthritis （CIA） model rats， and to investigate potential mechanism of anti-rheumatoid arthritis （RA）. METHODS： Totally 60 male SD rats were randomly divided into blank group， model group， positive group （Tripterysium glycosides tablets， 10 mg/kg）， A. chinense water extract low-dose， medium-dose and high-dose groups （5， 10， 20 g/kg， by crude drug）， with 10 rats in each group. Except for blank group， CIA model was established by giving Bovine type Ⅱ collagen emulsified with Freund’s complete adjuvant via tail. On the tenth day after modeling， medication groups were given the relevant medicine intragastrically， while blank group and model group were given constant volume of normal saline intragastrically， once a day for consecutive 2 weeks. General information， arthritis index （AI） and plantar swelling degree were recorded in each group. The serum levels of IL-1β and TNF-α were determined by ELISA. The mRNA expression of OPG， RANKL and RANK in synovium were determined by RT-PCR. The pathological changes of the ankle joint were observed by HE staining. RESULTS： Three rats in A. chinense water extract high-dose group died， while one in positive group and one in A. chinense water extract medium-dose group failed to establish the model. After modeling， other groups suffered from different degree swelling of plantar and ankle joints. Compared with blank group， AI， plantar swelling degree， serum levels of IL-1β and TNF-α， mRNA expression amount of RANKL and RANK in synovium were increased significantly， while mRNA expression amount of OPG was decreased significantly （P＜0.01）. Compared with model group， AI （28 d after modeling）， plantar swelling degree （21， 28 d after modeling）， serum levels of IL-1β and TNF-α， mRNA expression amount of RANKL and RANK in synovium were decreased significantly， while mRNA expression amount of OPG was increased significantly （P＜0.05）. AI， serum level of IL-1β and mRNA expression amount of RANKL in A. chinense water extract high-dose group as well as mRNA expression amount of RANK in A. chinense water extract medium-dose and high-dose groups were all significantly lower than positive group. Serum levels of TNF-α in positive group and A. chinense water extract high-dose group were significantly lower than A. chinense water extract low-dose and medium-dose groups （P＜0.05 or P＜0.01）. In blank group， the surface of the ankle joint was smooth， the synovial cells did not proliferate， and no inflammatory cell infiltration was observed. In model group， articular space became narrow， articular cartilage degenerated， synovial cells proliferated， local bone destruction and inflammatory cell infiltration were observed. The above symptoms of medication groups were improved to varying degrees. CONCLUSIONS： A. chinense water extract can relieve the arthritis reaction， degeneration of articular cartilage and bone destruction in CIA model rats， the mechanism of which may be related to reduce the serum levels of IL-1β and TNF-α， and regulate OPG/RANKL/RANK system.