Objective:To investigate the levels and the clinical signficance of matrix metalloproteinase 3 (MMP-3) in different activities of rheumatoid arthritis (RA).Methods:Case-control study. A total of 130 patients [24 cases of male, 106 cases of female, age (52.98±13.24)years, the median age was 51 years] with RA diagnosed in the Department of Rheumatology from the Second Affiliated Hospital of Soochow University, Suzhou Hospital of Traditional Chinese Medicine and Suzhou Ninth People′s Hospital from 2017 to 2018, and 100 healthy controls [28 cases of male, 72 cases of female, age (45.04±11.55) years, the median age was 44 years] from the physical examination center of the Suzhou Ninth People′s Hospital. The basic clinical data was used to determine the MMP-3 on groups of RA patients and healthy controls by immunoturbidimetry. The discriminating validity of MMP-3 in disease was evaluated using receiver operating characteristic (ROC) curve analysis.Results:Compared with that in healthy controls[28.0 (21.7-36.1)ng/mL], the MMP-3 in the low groups [51.8(41.8-73.1)ng/mL] increased dramatically ( Z=2.942, P<0.01). However, there was no significant difference between the MMP-3 in remission patients [28.8 (21.9-38.7)ng/mL] compared with the healthy controls ( Z=1.09, P>0.05). The area under the curve (AUC) of MMP-3 for diagnosis of RA was 0.877. the sensitivity was 73.1%, and the specificity was 93%.The AUC of MMP-3 diagnosis of low groups was 0.906, the sensitivity was 77.8%, and the specificity was 88%. In addition, the MMP-3 level was correlated with CRP and ESR ( r=0.242, r=0.243), and it was significantly correlated with DAS 28 ( r=0.361). Conclusions:It was indicated that the level of MMP-3 increased with the severity of rheumatoid arthritis. And the clinically low level of MMP-3 in RA patients could be used to indicate the remission condition. Meanwhile, the serum MMP-3 was closely related to DAS28.