Abstract: Objective To investigate the correlation among serum levels of manning-binding lectin (MBL), MBL-associated serine proteases-2 (MASP-2), complement C3 and high-sensitive C reactive protein (HsCRP) in patients with rheumatoid arthritis (RA). Methods Fasting venous blood were collected from 50 RA patients (25 in active stage and 25 in remission) and 40 healthy subjects for detecting serum levels of MBL, MASP-2, complement C3 and HsCRP using enzyme-linked immunosorbent assay (ELISA) and immune turbidity assay. Results The serum levels of MBL and MASP-2 were significantly lower and HsCRP level was significantly higher in patients with RA (in both acute stage and remission) than in the healthy control group (P<0.05), but complement C3 level was similar between the RA patients and control group. Bivariate Pearson correlation analysis showed that in RA patients, MBL was positively correlated with MASP-2 level (r=0.550, P=0.001) and negatively with HsCRP (r=-0.323, P=0.022) but not correlated with C3 (r=-0.022, P=0.882); MASP-2 was negatively correlated with HsCRP (r=0.453, P=0.453) and was not correlated with C3 (r=0.049, P=0.738). ROC curve analysis revealed the largest area under curve (AUC) of HsCRP (0.844, P=0.001) and smaller AUCs of MBL (0.025, P=0.001) and MASP-2 (0.266, P=0.001). HsCRP had a much higher sensitivity (84%) than MBL (10%) and MASP-2 (40%) in the diagnosis of RA. Conclusion In RA patients, MBL and MASP-2 are negatively correlated with HsCRP level. Serum MBL and MASP-2 levels decrease with the progression of joint injury in RA patients, suggesting their involvement in the pathological process of RA; but due to their low sensitivity, they are not appropriate indicators for evaluating the disease activity of RA.