This paper presents the actual status of species diversity of the phyla Cnidaria and Ctenophora along the Turkish coasts of the Black Sea, the Sea of Marmara, the Aegean Sea, and the Levantine Sea. A total of 195 cnidarian species belonging to 5 classes (Hydrozoa, Cubozoa, Scyphozoa, Staurozoa, and Anthozoa) have been determined in these regions. Eight anthozoan species (Arachnanthus oligopodus, Bunodactis rubripunctata, Bunodeopsis strumosa, Corynactis viridis, Halcampoides purpureus, Sagartiogeton lacerates, Sagartiogeton undatus, and Pachycerianthus multiplicatus) are reported for the first time as elements of the Turkish marine fauna in the present study. The highest number of cnidarian species (121 species) was reported from the Aegean Sea, while the lowest (17 species) was reported from the Black Sea. The hot spot areas for cnidarian diversity are the Prince Islands, Istanbul Strait, Izmir Bay, and Datca Peninsula, where relatively intensive scientific efforts have been carried out. Regarding ctenophores, 7 species are distributed along the Turkish coasts, 5 of which were reported from the Black Sea. A total of 16 alien cnidarian and 2 ctenophore species were determined in the regions. Two species (Sagartiogeton laceratus and Pachycerianthus multiplicatus) are new alien species for the Mediterranean Sea and could have been introduced to the northern part of the Sea of Marmara and Iskenderun Bay, areas from which these species are recorded, by ships from the North-East Atlantic.