Cudraflavone B (1) is a prenylated flavonoid found in large amounts in the roots of Morus alba, a plant used as a herbal remedy for its reputed anti-inflammatory properties. The present study shows that this compound causes a significant inhibition of inflammatory mediators in selected in vitro models. Thus, 1 was identified as a potent inhibitor of tumor necrosis factor α (TNFα) gene expression and secretion by blocking the translocation of nuclear factor κB (NF-κB) from the cytoplasm to the nucleus in macrophages derived from a THP-1 human monocyte cell line. The NF-κB activity reduction resulted in the inhibition of cyclooxygenase 2 (COX-2) gene expression. Compound 1 acts as a COX-2 and COX-1 inhibitor with higher selectivity toward COX-2 than indomethacin. Pretreatment of cells by 1 shifted the peak in an regulatory gene zinc-finger protein 36 (ZFP36) expression assay. This natural product has noticeable anti-inflammatory properties, suggesting that 1 potentially could be used for development as a nonsteroidal anti-inflammatory drug lead.