Catechol-O-methyltransferase (COMT) is a ubiquitous enzyme that catabolyzes catecholamines. Reduction in COMT activity results in increased pain sensitivity in animal models. In present study, we hypothesized that regulation of COMT expression could contribute to development of inflammatory pain. COMT is highly expressed in neurons and astrocytes, cells, playing the major role in pain response. We cloned a distal promoter of human COMT (P2-COMT) into a luciferase reporter vector and transiently transfected the construct into H4 astroglioma cells and PC-12 cells (a model of neuronal cells). We showed that proinflammatory cytokine tumor necrosis factor α (TNFα) down-regulated the activity of P2-COMT construct in both cell lines. After TNFα treatment, endogenous COMT was decreased on both mRNA and protein levels in primary astrocytes, PC-12 and H4 astroglioma cells. We then proposed that this TNFα-dependent regulation of COMT expression was mediated by activation of nuclear factor κB (NF-κB), the crucial regulator of inflammation and one of the major targets of TNFα. In support of this hypothesis, cotransfection of P2-COMT reporter construct with either p65 NF-κB subunit or IKKβ subunit expression constructs led to strong repression of luciferase activity and selective NF-κB inhibitor PDTC blocked TNFα-mediated down-regulation of the P2-COMT construct. Besides, TNFα-dependent suppression of endogenous COMT expression and P2-COMT construct activity was abrogated in H4 cells stably expressing IκBα super-repressor. Further experiments demonstrated that NF-κB down-regulation of P2-COMT was mediated by change in histone acetylation pattern. Collectively, these data strongly suggest that COMT is down-regulated by NF-κB pathway and that inflammation can lead to enhanced pain sensitivity through decreased COMT expression.