Abstract： Objective To investigate the expression of miR-155 and miR-146a in peripheral blood mononuclear cells (PBMC) and plasma of rheumatoid arthritis (RA) patients.Methods PBMC and plasma were separated from the peripheral blood of 34 RA patients and 15 healthy individuals.Total RNAs were isolated and miRNAs were purified.The levels of miR-155 and miR-146a were determined by quantitative reverse transcription PCR (qRT-PCR).U6 was used as housekeeping control.The amount of target miRNA was normalized relative to the amount of U6 (ΔCt=ΔCtmiRNA-ΔCtU6).Relative expression levels were expressed as 2 △-ΔCt.Data were analyzed using SPSS 13.0 software.The test of homogeneity of variance and unpaired t-test was used to compare between groups.P values (2-tailed) less than 0.05 were considered as statistically significant.Results The expressions of PBMC and plasma miR-155 were higher in RA patients than those in the healthy control individuals (0.08±0.08 vs 0.05±0.03,t=-2.225,P＜0.05; 5.9±6.7 vs 1.3±2.0,t=-3.677,P＜0.05).The expression of miR-146a in PBMC and plasma of RA patients and controls were (1.3±1.2 vs 0.8±0.6,t=-2.154,P＜0.05)and (741±1001 vs 300±295,t=-1.669,P＞0.05).According to their DAS28 value,RA patients were divided into high activity group (23 cases,DAS28≥5.0) and low disease activity group( 11cases,DAS28＜5.0).The plasma miR-155 and miR-146a expressions were significantly higher in high activity group than those in low activity group.There were no significant differences in the expression of PBMC miR-155 and miR-146a between the two groups.Conclusion The expression of PBMC and plasma miR-155 and miR-146a are higher in RA patients.The expression of plasma miR-155 and miR-146a are associated with RA patients' activity.Plasma miR-155 and miR-146a may be potential non-invasive biomarkers for RA diagnosis anddisease activity assessment.