For the first time the fatty acid content and composition of freshwater planarian Dendrocoelopsis sp. has been studied in a station of the large Siberian River, the Yenisei. The dominant fatty acids were palmitic, oleic, eicosapentaenoic and docosapentaenoic acids. The main peculiarity of the planarian fatty acid composition was the high relative content of docosapentaenoic acid, 22:5ω3, compared to other polyunsaturated fatty acids (PUFAs). The average content of ω3 PUFA in the planarian was significantly higher then that of ω6 PUFA, 7.20±1.21 and 1.22±0.22 mg/g of wet weight, respectively. The content of sum ω3 PUFAs which are essential for the nutrition of aquatic organisms of the higher trophic levels in the studied planarian was comparatively high.