Telestes karsticus is the freshwater fish from the family Cyprinidae, order Cypriniformes. This newly described, stenoendemic species of the Danube basin has a small distributional range. It was found only in Croatia where it has been recorded at only three localities around Velika and Mala Kapela mountains. The aim of this study was to determine qualitative and quantitative diet composition of the Telestes karsticus in order to obtain fundamental knowledge about the feeding ecology of species, which will directly affect and improve their protection. In order to gain insight into the dietary habits throughout the year, fish and macrozoobenthos samples were collected throughout all four seasons (spring, summer, autumn, winter) during 2007./2008. at the Sušik Creek in Lug Field placed between Velika and Mala Kapela mountains. Analysis of the diet was conducted on a sample of 84 individuals. According to the results Telestes karsticus is euryphagous omnivore whose diet composition includes both plant and animal components but also show the tendency towards cannibalism. The most abundant dieting group are water invertebrates. The composition of the Telestes karsticus diet includes nine classes of macroscopic invertebrates, seven of which are made of water invertebrates. The dominant dieting elements throughout the year are groups of organisms of the order of Diptera. The larvae of Chironomidae are numerically the most abundant and most freaquent pray in the fishes digestive system. The most abundant dieting element varies throughout the year. During the Spring and the Summer time Chirinomidae larvae prevail. The Fall season is represented by Cladocera plankton and Ephemeroptera larvae, while the Winter period is characterized with Hydracarina, Cladocera and Oligochaeta.