Abstract：Objective：To discuss naringin improving imbalance of regulatory T cells(Treg)/helper T cells 17(Th17) in rats with rheumatoid arthritis(RA) by up-regulation of miR- 21. Methods：Male SD rats were divided into the control group，the model group，the dexamethasone group and the naringin group of low- dose，middle- dose and high- dose. Except in the control group，rat models with type Ⅱ collagen-induced arthritis(CIA) were established in the other groups. After successful establishment，the dexamethasone group was given 2 mg/kg dexamethasone in aqueous solution；the naringin groups were given 15 mg/kg，30 mg/kg and 60 mg/kg naringin in aqueous solution respectively；the control group and the model group were given distilled water of same volume. After four weeks of intervention， the rate of swelling joint and pathological changes of synovial tissue of joint were observed；the mRNA expression of miR- 21，forkhead transcription factors(Foxp3) and retineic- acid- receptor- related orphan nuclear receptor gamma(ROR- γt) in rat's blood， as well as the levels of interleukin-10(IL-10) and interleukin-17(IL-17) in synovial fluid were detected. Results：When compared with those in the control group， in the model group， there were significant synovial hyperplasia in knee joint， inflammatory cell infiltration， joint function decrease，increasing swelling joint rate and rising levels of ROR- γt mRNA in blood and IL-17 in synovial fluid (P＜0.05)； the mRNA expression of miR- 21 and Foxp3 in blood and the level of IL- 10 in synovial fluid in the observation group were decreased(P＜0.05). When compared with those in the model group，synovial hyperplasia and inflammatory cell infiltration in the dexamethasone group were significantly decreased；in the naringin groups，the degree of inflammatory cell infiltration and synovial hyperplasia were lower， with a dose- dependent manner. In the dexamethasone group and the naringin groups，the rates of swelling joint，the mRNA expression of ROR-γt in blood and the level of IL-17 in synovial fluid were significantly decreased(P＜0.05)；the mRNA expression of miR-21 and Foxp3 in blood as well as the level of IL-10 in synovial fluid were significantly inincreased(P＜0.05)；in the naringin groups of different doses，there were dose-dependent manners(P＜0.05). Conclusion：Naringin can inhibit inflammatory reactions of CIA rats，as well as regulate the imbalance of Treg/ Th17 and protect RA through the up-regulation of miR-21，which indicates that naringin can be applied to RA treatment as a kind of medicine for immunosuppression and cartilage protection.