This work aimed to reveal the invasive mechanism of invasiv plant species and to study their beneficial uses. An acetylcholinesterase inhibitor linarin was isolated from Buddleja davidii Franch (Buddlejaceae), and the structure-activity relationship was studied. HPLC/UV/ESI-MS analyses demonstrated different phytochemcial profiles of Polygonum cuspidatum Sieb. & Zucc. and P. sachalinensis F. Schmidt ex Maxim (Polygonaceae) from China and Switzerland. Seven compounds of 21 isolated compounds were reported for the first time from these two species. Allelopathy tests revealed strong phytotoxicity of the leaf and root extracts, and discovered two strong allelochemicals resveratrol and rhein, as well as piceid, resveratroloside or piceatannol glucoside with stronger activity than (-) - catechin. Other biotests showed the potential of the isolated compounds against α-glucosidase, aromatase or as anti-inflammatory agents. At last the total content of resveratrol in the invasive Swiss variety of P. cuspidatum was measured to prove it a source of resveratrol.