Abstract： Objective To study the clinical significance of matrix metalloproteinase-9(MMP-9),tissue inhibitor of metalloprotenases(TIMPs)and transforming growth factor beta 1(TGF-β1)in the serum of patients with rheumatoid arthritis(RA)associated interstitial lung disease(ILD). Methods Twenty-nine patients with RA only(the RA group)and 28 patients with RA associated ILD (the RA-ILD group)were included in the study.Patients in the RA-ILD group were divided into 2 subgroups,16 in the early RA-ILD group and 12 in the late RA-ILD group.Twenty-nine healthy volunteers senred as the control group.ELISA was used to detect the levels of MMP-9,TIMP-1,TGF-β1 in the serum of the three groups.Results The TIMP-1 levels of both the RA and the RA-ILD groups[(645±220)μg/L,(536±188) μg/L]were significantly higher than that of the control group[(392±92)μg/L,F=15.221,P＜0.01].The TGF-β1 level of the RA-ILD group[(13.1±10.0)μg/L]was significantly higher than those of the control group and the RA group[(3.9±2.9)μg/L,(2.4±1.7)μg/L,F=26.455,P＜0.01].There was no difierence in the TIMP-1 level between RA-ILD and RA groups,the TGF-β1 level between the control group and the RA group,the MMP-9 level and MMP-9/TIMP-1 ratio among the three groups.The TIMP-1 level in the late RA-ILD group[(690±110)μg/L]was higher than that of the early RA-ILD group[(420±147)μg/L,t=-5.347,P＜0.01].The TGF-β1 level in the late RA-ILD group[(17.9±8.2)μg/L]was higher than that of the early RA-ILD group[(9.5±9.9)μg/L,t=-2.39,P＜0.05].The MMP-9/TIMP-1 ratio of the late RA-ILD group(0.9±0.1)was lower than that of the early RA-ILD group (1.2±0.4,z=4.307,P＜0.01).There was no statistic significance in the MMP-9 level between the early and the late RA-ILD groups[(537±309)μg/L,(595±110)μg/L,t=-1.397,P=0.174].Conclusions TGF-β1 can be used as a diagnostic marker of ILD in RA patients and it also reflects the pathological change of the lung.The decrease of MMP-9/TIMP-1 ratio in RA patients with ILD can reflect the severity degree of lung pathological changes.