The round goby Neogobius melanostomus is a bottom-dwelling fish native for the Ponto-Caspian basin, which started to colonize the Baltic Sea since 1991. The parasites of this fish species in the southwestern Baltic region are studied for the first time. The round goby in the SW Baltic Sea was infected with 12 parasite species: 1 species of Microsporidia, 1 species of Monogenea, 1 of Cestoda, 3 species of Trematoda, 3 species of Nematoda, 2 of Acanthocephala, and 1 species of Bivalvia. Microsporidia genus species have the great tendency to join the infracommunity in all localities, except the Stettiner Haff, where this tendency have Diplostomum spathaceum met and Unio sp. glochidia. The round goby was colonized by seven new parasites species not found in this fish in the Baltic Sea earlier: Microsporidia gen. sp., Gyrodactylus rugiensis, Bucephalus polymorphus, Cosmocephalus obvelatus L3, Eustrongylides excisus L3, Paracuaria adunca L3, Unio sp. glochidia. Microsporidia gen. sp., G. rugiensis, and Unio sp. are new parasites for the round goby. In general, the processes of colonization have the same tendency as in the Gulf of Gdańsk.