Adriatic Sea is small and enclosed oligotrophic sea, but because of the specific conditions that made its northern part one of the most productive areas of Mediterranean sea and its indented coastline, it is home to large number of species. Among them there are marine mammals, mostly from the order of whales (Cetacea). The only species that belongs to the superfamily of seals (Pinnipedia) is the Mediterranean monk seal. The common bottlenose dolphin (Tursiops truncatus), the short-beaked common dolphin (Delphinus delphis), the striped dolphin (Stenella coeruleoalba), the fin whale (Balaenoptera physalus), the Risso's dolphin (Grampus griseus) and the Cuvier’s beaked whale (Ziphius cavirostris) are the six most important species in the Adriatic. Besides them, the sperm whale (Physeter macrocephalus), the long-finned pilot whale (Globicephala melas), the false killer whale (Pseudorca crassidens) and the humpback whale (Megaptera novaeangliae) are occasionally seen species that have no suitable habitat in the Adriatic. This thesis contains common knowledge about marine mammal groups and species of Adriatic Sea and discusses reasons for their endangerment. All discussed species are under some form of a threat, but the scientists can't see the big picture because of the lack of information about their abundance. To save these species, it is necessary to introduce more rigorous means of protection.