Two new polyacetylenes, oploxynes A (1) and B (2), and the known oplopandiol (3) and falcarindiol (4) were isolated from the stem of Oplopanax elatus. The structures of compounds 1 and 2 were determined to be 9,10-epoxyheptadeca-4,6-diyne-3,8-diol and 10-methoxyheptadeca-4,6-diyne-3,8,9-triol, respectively, on the basis of their UV, MS, and NMR data. The absolute configurations of these compounds were determined using the modified Mosher's method and acetonide formation. Oploxyne A (1), oplopandiol (3), and falcarindiol (4) inhibited the formation of nitric oxide (NO) and prostaglandin E(2) (PGE(2)) in lipopolysaccharide (LPS)-induced murine macrophage RAW 267.7 cells.