Objective To investigate the relationship between serum matrix metalloproteinase-3 and rheumatoid arthritis. Methods The serum MMP-3 level in 146 patients with RA and 232 non RA patients were detected by immunoturbidimetry. The receiver operating Curve (ROC) analysis was carried out to get the cut-off value. The relationship between MMP-3 and other clinical biochemical indices were analyzed by multiple regressions. Results The serum MMP-3 concentration in RA group (170±19.36 ng /mL) was significantly higher than that of control group (47.92±1.98 ng /mL)（P＜0.001). The optimal diagnostic cut-off value for MMP-3 was 71.65 ng/mL. The sensitivity and specificity were 58.9% and 88.79% respectively at this cut-off value. The serum concentration of MMP-3 in RA patients was significantly correlated with inflammation and activity indices such as C-reaction protein, prealbumin, erythrocyte sedimentation rate, platelet, white blood cell count (P<0.001). Conclusion The serum MMP-3 levels in patients with rheumatoid arthritis is correlated to inflammatory activity.