This study shows that Tapinanthus pentagonia, phanerogam parasite of the family Loranthaceae is widespread in Mauritania and is also used by the Mauritanians to relieve conditions such as infertility, jaundice and kidney stones which attests of its medicinal properties. This phanerogam is also much sought after by livestock. In addition, our phytochemical study on the leaves of T. pentagonia parasite of Acacia tortilis shows the presence of flavonoids, tannins, ellagic acid, proanthocyanidols of saponins, sterols, polyphenols, reducing sugars and terpenes. We have also shown that the presence and distribution of these metabolites known to be responsible for the antioxidant activity of plants, in T. pentagonia are closely related to the nature of the host. The antibacterial activities of the aqueous extracts revealed activity against S auere at different degrees.