Eighteen lignans were isolated from an ethanol extract of Machilus robusta by a combination of various chromatographic techniques including column chromatography over silica gel, Sephadex LH-20 and reversed-phase HPLC. Their structures were identified by spectroscopic data analysis as isolariciresinol-9'-O-beta-D-xylopyranoside (1), (+)-5'-methoxy-isolariciresinol-9'-O-beta-D-xylopyranoside(2), lyoniresinol-9'-O-beta-D-xylopyranoside(3), (+)-(8S, 8'S) -4, 4'-dihydroxy-3, 3', 5, 5'-tetramethoxylignan-9, 9'-diol 9-O-beta-D-xylopyranoside (ssioriside, 4), lyoniresinol (5), meso-dihydroguaiaretic acid (6), (+)-(8S, 8'R)-3', 4, 4'-trihydroxy-3'-methoxylignan (7), (8S, 8'R)-4'-hydroxy-3, 3', 4-trimethoxylignan (meso-monomethyl dihydroguaiaretic acid, 8), (+)-guaiacin (9), isoguaiacin (10), (-)-(7'R, 8R, 8'R)-4, 4'-dihydroxy-3, 3', 5-trimethoxy-2, 7'-cyclolignan (11), henricine B (12), (-)-(7S, 7'S, 8R, 8'R)-4, 4'-dihydroxy-3, 3', 5, 5'-tetramethoxy-7, 7'-epoxylignan-9, 9'-dio] (7S, 7'S, 8R, 8'R-icariol A2, 13), (+)-(7R, 8R, 7'E)-4-hydroxy-3, 5'-dimethoxy-7, 4'-epoxy-8, 3'-neolignan-7'-ene (licarin A, 14), nectandrin B (15), machilin-I (16), (-)-pinoresinol (17), and (-)-syringaresinol (18). All compounds were isolated from this plant for the first time. In the preliminary assay, compound 17 showed inhibitory activity against NO secretion of mouse peritoneal macrophages with an inhibition rate of 72.2% at 10 micromol x L(-1).