OBJECTIVE： To investigate the effects of the ethanol extract of Tibetan medicine Gentiana straminea （GSM） on the expression of NF-κB p65 in synovial tissue of collagen-induced arthritis （CIA） model mice， and to provide a reference for elucidating the action mechanism of its anti-rheumatoid arthritis （RA）. METHODS： Totally 40 mice were randomly divided into normal group， model group， dexamethasone group （positive drug， 0.25 mg/kg） and GSM low-dose and high-dose groups （25， 50 mg/kg， calculated by crude drug）， with 8 mice in each group. Except for normal group， other groups were given intradermal injection of Chicken type Ⅱ collagen intracutaneously via tail to induce CIA model. After modeling， medication group was given relevant medicine intragastrically once a day， and normal group and model group were given same amount of normal saline intragastrically for consecutive 28 d. The arthritis index （AI） of mice were determined 7， 14， 28， 35 d after medication. After last medication， the spleen index and thymus index of mice were determined； ELISA was used to measure the serum levels of IL-1β， IL-6 and TNF-α； Pathological change of synovial tissue in ankle joint of mice was observed by HE staining； Western blot was used to detect the protein expression of NF-κB p65 in synovial tissue of mice. RESULTS： Compared with normal group， the levels of AI value after different medication time， and spleen index， thymus index， serum inflammatory factors （IL-1β， IL-6， TNF-α） and protein expression of NF-κB p65 in synovial tissue were increased significantly in model group （P＜0.05）. Pathological changes of synovial tissue in mice were observed， such as dense and disorder cell arrangement， the increase of synovial cells， hyperemia. Compared with model group， decrease of AI was not significant in GSM low-dose group 7， 14 d after medication， and other indexes of medication groups were all decreased significantly （P＜0.05）. The inflammatory cell hyperplasia and the number of inflammatory cells were decreased in medication groups. CONCLUSIONS： GSM can inhibit the protein expression of NF-κB p65 in synovial tissue and relieve synovial inflammation and play its role on the anti RA by reducing the levels of serum inflammatory factors.