Objective To observe the effects of intra-articular ozone injection on the secretion of tumor necrosis factor (TNF)-α,Interleukin (IL)-6,IL-17A,and vascular endothelial growth factor (VEGF) in the serum of rats with collagen-induced arthritis (CIA) and explore the therapeutic mechanism of ozone in RA treatment.Methods Thrity-two Wistar rats were randomized into 4 groups,including the ozone groups that receivedintra-articularinjection of 40 μg/ml ozone (O3 group),a blank control group (normal group),a methotrexate (MTX) group (MTX group) anda collagen-induced arthritismodel (CIA group).All the rats,except for those in the blank control group,were subjected to hypodermic injection of bovine collagen Ⅱ and complete Freund's adjuvant to induce CIA.Ozone treatment was administered once weekly for 3 weeks starting at 14 days after the model were established.MTX group were treated with methotrexate 0.9 mg/kg,once a week,a total of three weeks.The swelling degree of the foot were observed,and the serum contents of TNF-oα,IL-6,IL-17A and VEGF were detected.One-way analysis of variance or Kruskal-Wallis test was used to evaluate the experimental data.Results At the end of treatment,the degree of foot swelling was reduced significantly in rats with O3 group compared with that in the CIA group [(4.21±0.14) ml vs (9.12±0.17) ml,t=8.43,P=0.023].The serum concentration of TNF-α,IL-6 and VEGF showed significant difference between the CIA group and the O3 group[91.55(86.55,98.53) pg/ml vs 14.45 (12.55,16.15) pg/ml,x2=6.216,P=0.002;145.08(37.44± 362.82) pg/ml vs 5.84(5.47,15.93) pg/ml,x2=13.136,P=0.004;51.56(46.09,74.10) pg/ml vs.36.22(32.18,41.69) pg/ml,x2=3.732,P=0.002].There was no statistically significant difference between the O3 group and MTX group [14.45(12.55,16.15) pg/ml vs [12.45(11.80,15.60) pg/ml,x2=0.243,P＞0.05;5.84(5.47,15.93) pg/ml vs 7.86(5.25,15.23) pg/ml,x2=0.058,P＞0.05;36.22(32.18±41.69) pg/ml vs 40.17(35.47,50.73) pg/ml,x2=0.516,P＞0.05].The serum concentration of IL-17A showed no significant difference between the normal group,the CIAgroup,the MTX group and the O3 group (F=1.827,P=0.165).Conclusion Intra-articular injecfion of 40 μg/ml ozone can attenuate synovitis in rats with CIA,the mechanism may relate to the inhibition of TNF-oα,IL-6 and VEGF in the serum.