A novel bibenzyl, a new bibenzyl, two new phenanthrenes, and a new lignin glycoside, namely longicornuol A (1), 4-[2-(3-hdroxyphenol)-1-methoxyethyl]-2,6-dimethoxyphenol (2), 5-hydroxy-7-methoxy-9,10-dihydrophenanthrene-1,4-dione (3), 7-methoxy-9,10-dihydrophenanthrene-2,4,5-triol (4) and erythro-1-(4-O-beta-D-glucopyranosyl-3-methoxyphenyl)-2-[4-(3-hydroxypropyl)-2,6-dimethoxyphenoxy]-1,3-propanediol ( 5), together with 14 known compounds, were isolated from the stems of Dendrobium longicornu. All structures were elucidated by spectroscopic methods (NMR, MS, UV and IR). Anti-platelet aggregation activities of compounds 1 - 5 were also tested.