Genus Alnus are deciduous board-leaved trees or shrubs found in the damp place and mountain and more than 17 species are growing in Korea. The bark of Alnus japonica has been used for the treatment of fever, hemorrhage and diarrehea in oriental traditional medicine. Quantitative analysis of diarylheptanoids which were characteristic components of Alnus species (A. japonica, A. hirsuta, and A. hirsuta var. sibirica), has been conducted by HPLC. The results showed that these plants were rich source of diarylheptanoids and the amount of oregonin and hirsutanonol which were major diarylheptanoids showed seasonal variation.