Eurycomalactone is a natural product isolated from Eurycoma longifolia Jack., acts as a potent NF-kappaB inhibitor( IC50 of 0.5 µM). Eurycomalactone inhibits protein synthesis, depletes cyclin D1, but does not affect TNFalpha-induced degradation of IkappaBalpha or the phosphorylation of IKKalpha/beta and IkappaBalpha.