The aim of this study was to analyze the natural food diet composition of pike introduced and naturalized in the upper course of the Vrljika River. In February 2020., 38 individuals of pike were collected. Digestion was isolated from each individual by cutting the esophagus and anal opening. The individuals analyzed were determined to the class and level of order. Out of a total of 38 analyzed pike, 17 (44,74%) of them had a full and 21 (55,26%) had an empty stomach. In order to gain an insight into the qualitative and quantitative composition of the diet of pike in Vrljika, the percentage of abundance (%N), the percentage of frequency of occurrence (%F), the percentage of mass (%W) and the relative importance index (%IRI) were calculated. The calculation results of the mentioned methods show that pike prefers different prey depending on the body length. Pike with a total body length of less than 50 cm prefer fish as their prey, while for pike with total body length of less than 50 cm, crustaceans from the order Amphipoda and Isopoda are the most important in their diet. Three types of fish have been found in the diet of pike in Vrljika river, two of them are endemic; basak (Rutilus basak) and spotted minnow (Delminichthys adspersus), and pike (Esox lucius) which confirmed cannibalism in pike.