A growing number of studies suggest that synovitis plays an important role in the pathogenesis and progression of osteoarthritis (OA). As a negative mediator of the nuclear factor-kappa B (NF-kappa B) signaling pathway, the zinc finger protein A20 has significant anti-inflammatory properties. In this study, the differential expression of A20 was investigated at the mRNA and protein levels in human normal OA fibroblast-like synoviocytes (FLSs) and normal FLSs pretreated with TNF-alpha. We then measured the activation of the NF-kappa B pathway and expression of pro-inflammatory cytokines in the above three groups by western blotting, a human cytokine array and ELISA. We found that TNF-alpha, activated the NF-kappa B pathway, increased the expression of the pro-inflammatory cytokines IL-6 and IL-8, and A20 expression in human normal FLSs. However, the role of A20 in FLSs was unclear. To clarify this, we investigated the effect of A20 overexpression in human normal FLSs. The results indicate that A20 inhibits the NF-kappa B signaling pathway activation and OA-associated pro-inflammatory cytokines release. The results of this study indicate that A20 has anti-inflammatory effects in FLSs, which makes it a potential target for OA synovitis treatment. (C) 2018 Elsevier Inc. All rights reserved.