OBJECTIVE.: MicroRNAs are recognized as important regulators of a variety of fundamental biological processes. Previously, we described increased expression of miR-155 and miR-146a in rheumatoid arthritis (RA) and showed a repressive effect of miR-155 on MMP expression in RA synovial fibroblasts (RASFs). Now, we found altered expression of miR-203 in RASFs and analyzed its role in activation of fibroblasts. METHODS.: Differentially expressed miRNAs in RASFs versus osteoarthritis (OA) SFs were identified by Real-time PCR-based miRNA screening of 260 individual miRNAs. Transfection of precursor miRNAs pre-miR-203 was used to analyze the function of miR-203 in RASFs. Levels of IL-6 and matrix-metalloproteinases were measured by Real-time PCR and ELISA. RASFs were stimulated with IL-1β, TNFα, LPS and 5-azacytidine. Activity of IkappaB kinase 2 was inhibited with SC-514. RESULTS.: Expression of miR-203 was higher in RASFs than in OASFs or healthy donors. Stimulation with neither IL-1β, TNFα nor LPS changed levels of miR-203, however, DNA demethylation with 5-azacytidine increased the expression of miR-203. Enforced expression of miR-203 led to significantly increased levels of MMP-1 and IL-6. Induction of IL-6 by miR-203 overexpression was inhibited by blocking of the NF-κB pathway. Basal expression levels of IL-6 correlated with basal expression levels of miR-203. CONCLUSION.: In the current study, we demonstrate methylation dependent regulation of miR-203 expression in RASFs. Importantly, we show that elevated levels of miR-203 lead to increased secretion of MMP-1 and IL-6 via the NFkB pathway and thereby contribute to the activated phenotype of synovial fibroblasts in RA.