A diarylheptanoid, (5S)-1,7-bis-(3,4-dihydroxyphenyl)-5-hydroxyheptane-3-on-5-O-β-D-xyiopyranoside, named as oregonin (1), was isolated from the bark of Alnus tinctoria Sarg. which is a species of the genus Alnus species, growing throughout Korea. The structure elucidation was accomplished by various spectroscopic methods including Negative FAB-MS, 1H-NMR and 13C-NMR techniques or comparison with authentic samples.