Bidens pilosa is a cosmopolitan, annual herb which originates from tropical and Central America. Its hardiness, explosive reproductive potential, and ability to thrive in almost any environment have enabled it to establish throughout the world. Generally introduced unintentionally through agriculture or sometimes intentionally for ornamental purposes, B. pilosa is a major crop weed, threat to native fauna, and a physical nuisance. It is considered one of the most noxious annual weeds in East Africa. B. pilosa had strong allelopathic effects which is beneficial in enhancing its capacity in interspecific competition and to promote its invasion. It is used as a folkloric medicine for the treatment of various diseases and used extensively by indigenous people, especially in Africa, for the treatment of a variety of ailments. Various compounds with biological activity, mainly, polyacetylenes and flavonoids have been isolated and identified in all parts of the plant. Pharmacognostic studies and phytochemical screenings of B. pilosa had also shown the presences of other compounds with biological activities which include terpenes, essential oils, tannins, polysaccharides, phenols, amino acids, ascorbic acid and organic acids. These plants are ingested as decoctions, teas and juice preparations to treat respiratory infections as well as various other ailments. Aqueous extract of the leaves is used by the Zulu tribe in South Africa for treating dysentery, diarrhea and colic. Juice preparations are also made into a poultice and applied directly on the infected wounds or burns. The widespread use of B. pilosa both in Africa and the rest of the world indicate that this plant may yield valuable drugs to treat a variety of different ailments such as malaria. Although considered an invader in many countries, the potential benefit may outweigh the risks that the weed poses to the environment. Key words: Bidens pilosa, medicinal properties, black jack.