Alnus japonica has been known to exert antioxidative, anti-inflammatory, anti-cancer and immune response inhibitory effects. The aim of this study was to figure out the characteristics of extracts obtained with different extraction solvent such as water, 100% ethanol, 70% ethanol or 70% methanol because characteristic components such as oregonin and hirsutanone extracted from Alnus japonica might be essential for the biological activity. For this purpose, oregonin and hirsutanon of four extracts, index ingredient of Alnus japonica, were analyzed with HPLC and physicochemical studies such as SEM, particle size and zeta potential were conducted. In cell cytotoxicity study, extract of water showed the highest cytotoxicity among four extracts. In case of oregonin, 70% MeOH and water extracts showed high contents and in case of hirsutanone, all extracts showed similar contents except 70% EtOH extracts. The extract of 70% MeOH from Alnus japonica for both oregonin and hirsutanone appeared to have the highest content. Both oregonin and hirsutanone extracted from Alnus japonica using 70% methanol showed stability in pH 1.2.