Nuclear factor-κB (NF-κB) and the signaling pathways that regulate its activity have become a focal point for intense drug research and development efforts. NF-κB regulates the transcription of a large number of genes, particularly those involved in immune, inflammatory, and anti-apoptotic responses. In our search for NF-κB inhibitors from natural resources, we identified malloapelta B as an inhibitor of NF-κB activation from Mallotus apelta Muell-Arg. In the present study, we demonstrated the effect of malloapelta B on NF-κB activation in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. This compound suppressed NF-κB activation through the inhibition of IκB kinase (IKK) activation, thereby blocking the phosphorylation and degradation of the inhibitor of NF-κB alpha (IκBα), and the nuclear translocation and DNA-binding activity of p65. The suppression of NF-κB by malloapelta B led to the down-regulation of target genes involved in inflammation and proliferation. Taken together, this study extends our understanding on the mechanisms underlying the possible anti-inflammatory and anti-cancer activities of malloapelta B. Our findings provide new insight into its mechanisms of action and propose a potential application of malloapelta B for inflammatory diseases as well as certain cancers associated with abnormal NF-κB activation.