Abstract This study was carried out in order to determine hydroid polyp species present in the Bosphorus and some ecological properties of. these species. Samples were collected at 19 stations from depths ranging 0.5- 60 m by using spatula, beam-trawl and dredge. As a result of this study, 14 species belonging to 10 genera and 6 families were determined and 4 species among them (Tubularia cf. indivisa Linnaeus, 1758, Halecium beanii (Johnston, 1838), Halecium labrosum Alder, 1859, Laomedea exigua M. Sars, 1857) were seen to be new records for the fauna of the Bosphorus, according to present literature.