AbstractSome holoparasitic species can become cultivated plants due to their unique chemical composition. A lot of bioactive contents are characteristic for them. Holoparasites of the family Orobanchaceae are known to be an important and rich source of polyphenols, especially metabolites of the phenylethanoid glycosides (PhGs) group. However, only a minority of the species in this family have been phytochemically tested. They are reported to have multiple biological and therapeutic effects and have been used for centuries in traditional Chinese medicine. This is the first study to present phytochemical profiling for a representative of genus Phelypaea. The chemical composition and biological activity in particular organs of the parasite, P. tournefortii, were determined. The interaction with its host, Tanacetum polycephalum (Asteraceae), from different places and altitudes was also studied. We presented the determination of polyphenolic compounds with the UPLC-PDA-MS/MS method, antioxidative effects and inhibitory activities, polyphenols, and nitrates content, ABTS•+, DPPH, FRAP, as well as colour parameters. The polyphenols profile of the parasite and host were different in quality and quantity. Identification of polyphenolic compounds revealed 41 compounds, 15 in the parasite (12 phenylethanoids and 3 anthocyanins), and 26 in the host (mainly flavonoids and phenolic acids). The amount and biological activity of polyphenolic compounds present in Phelypaea was very diverse and depended on the host plant and the parasite’s organs, as well as on population altitude. The results show that P. tournefortii is a potential source of functional and pro-health components. They also direct researchers’ attention to the parasite’s organs, host, and environmental influence.