Phenylbutenoids 1—6 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, 7 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, 1 and 2, exhibited considerable activity with IC₅₀ values of 2.71 and 3.64 μM. Two phenylbutenoid monomers, 3 and 4, showed moderate activity (IC₅₀ 14.97, 20.68 μM, respectively). The other three phenylbutenoids, 5—7, were found to be inactive. Compound 7 was elucidated as a new phenylbutenoid glycoside, namely, (E)-4-(3,4-dimethoxyphenyl)but-3-en-1-O-β-D-glucopyranoside by spectral analysis including various 1D- and 2D-NMR experiments.