Genus Rhizostoma is represented by the following species: Rhizostoma pulmo (Macri, 1778), Rhizostoma luteum (Quoy in Gaimard, 1827) and Rhizostoma octopus (Linnaeus, 1788). All three species are morphologically similar. The biggest difference among them is their geographic distribution. Because of small differences, dividing genus into three species is doubtfull according to some scientists. In this thesis we focused on clarification of genus phylogeny, phylogenetic structure of populations in Mediterranean Sea and their connection with Atlantic populations. In analysis samples of R. pulmo from Mediterranean Sea, R. luteum from Spanish coast and already sequenced samples of R. octopus from GenBank were used and compared. Target DNA segments were amplified with polymerase chain reaction. 28S, ITS1, ITS2 and COI regions were used in PCR. Results support division of genus Rhizostoma into three species which is the result of biogeographic events in the past and is maintained by Almeria-Oran front. Furthermore, Mediterranean populations are showing differences between populations from different locations.