A new scheme of the isolation of all fractions of polyphenolic compounds from wormwood-leaved ambrosia (Ambrosia artemisiifolia L.) collected in the budding period is proposed. The main components in the total extract are phenolcarboxylic acids (ferulic, isoferulic, caffeic, chlorogenic acids and caffeic acid glycoside) coumarins (scopoletin, scopolin, esculetin, esculin, umbelliferone, skimmin), and flavonoids (jaceidin, quercetin, isorhamnetin, isorhamnetin-3-rutinoside, quercimeritrin, isoquercitrin, and glycosides of xanthomicrol and 4¢,5-dihydroxy-3,6,7,8-tetramethoxyflavone). Polymethoxylated flavonoids have been identified in ambrosia and characterized for the first time, including jaceidin (5,7,4¢-trihydroxi-3,6,3¢trimethoxyflavone), xanthomicrol (4¢,5-dihydroxy-6,7,8-trimethoxyflavone), 4¢,5-dihydroxy-3,6,7,8-tetramethoxyflavone, and their glycosides. The results of biological investigations of the obtained polyphenolic fractions showed their pronounced hepatoprotective properties (exceeding those of the well-known drug karsil) and hypolipemic activity (comparable with that of lipanor).