The article is devoted to alien fish species that have appeared over the past 50 years off the coast of Ukraine in the Sea of Azov. The coastal waters of the Sea of Azov are analysed within the waters of Ukraine from Cape Tarkhan of the Kerch Peninsula to the Kryva Spit in Taganrog Bay with the selection of three areas: the southern part—from Cape Tarkhan to Cape Kazantip; the western part—from Arabatska Bay to the Tonka Strait, including Syvash Bay; the northern part—from the Utlyutsky Estuary to the Kryva Spit. According to generalised data from numerous literature sources, from the time of the publication of the work of K. F. Kessler in 1877 and A. Ostroumov in 1897 to the present time, 53 species of fish from 43 genera and 32 families of Atlantic–Mediterranean origin have been registered in the Sea of Azov. During the same period of time, 37 species from 32 genera and 25 families were recorded in the waters of Ukraine. From this list currently disappeared 4 species from 2 families. Since the 1970s, 6 alien species of Atlantic–Mediterranean origin (or complex) have been found in the waters of the Sea of Azov in Ukraine (11.3% of the total number of species registered in the sea since 1897), belonging to 6 genera of 6 families. At species level, aliens make up 16.2% of the number of representatives of the Atlantic–Mediterranean assemblage in Ukrainian waters, at the genus level—18.7%, and at family level—24.0%. According to ecological groups, 3 species belong to benthic species, 2 to bentho-pelagic species, and 1 to pelagic species. Brief information on these species is given (synonymy, presence of material in the fish collection of the National Museum of Natural History NAS of Ukraine, description, distribution, record localities). A table is provided with a complete list of species of this assemblage in Ukrainian waters and the entire Sea of Azov. Unlike other areas of the Azov–Black Sea Basin (Crimean waters, north-western part of the Black Sea), where a share of aliens has also occurred constantly and sporadically, all alien species of the Sea of Azov of Atlantic–Mediterranean origin over the past 50 years are random in the area that have entered the sea during intensive advection of saline Black Sea waters through the Kerch Strait.
