Phenylbutenoids isolated previously from the CHCl3 extracts of the rhizomes of Zingiber cassumunar, were evaluated for their cyclooxygenase-2 (COX-2) inhibitory activity along with a new isolate, from the n-BuOH extracts of this plant. The COX-2 inhibitory assay was performed by measuring prostaglandin E2 production in lipopolysaccharide-stimulated mouse macrophage RAW 264.7 cells. Two phenylbutenoid dimers, and, exhibited considerable activity with IC50 values of 2.71 and 3.64 microM. Two phenylbutenoid monomers, and, showed moderate activity (IC50 14.97, 20.68 microM, respectively). The other three phenylbutenoids, were found to be inactive. Compound was elucidated as a new phenylbutenoid glycoside, namely, (E)-4-(3,4-dimethoxyphenyl)but-3-en-1-O-beta-D-glucopyranoside by spectral analysis including various 1D- and 2D-NMR experiments.