Different Iris species are a rich source of secondary metabolites and they are widely used due to their medicinal properties, i.e. such as antibacterial, cytotoxic, hepatoprotective, antiplasmodial, and immunomodulatory effects. Determination of the fatty acid composition is necessary to create complex phytopreparations on their basis, and also, it is important for understanding of the adaptive capabilities of the plant. In our study, a comparative analysis of fatty acids composition of total lipids of the leaves and rhizomes of Iris sibirica was carried out by the gas chromatography-mass spectrometry method. The degree of unsaturated fatty acids and the activity of acyl-lipid desaturases were determined by the Lyons method. 14 fatty acids were identified in the leaves of I. sibirica, their content being 6.1 mg/g; 18 acids were found in the rhizomes, their content being 6.9 mg/g. Among the saturated fatty acids palmitic acid dominates (C16:0), and among the unsaturated ones, it is linoleic (C18:2ω6) and α-linolenic (C18:3ω3) acids. The content of the unsaturated fatty acids in the leaves is higher (45%) due to a high content of the polyunsaturated fatty acids, as well as the reduced share of the saturated and the monounsaturated acids, compared to the rhizomes (the content of the unsaturated fatty acids is 40%), which causes a higher value of the double bonds index (1.10), and the coefficient of unsaturation (0.81), which indicate the relative cold resistance of the plants. By contrast, in the rhizomes the concentration of the saturated fatty acids increases and the level of the unsaturated fatty acids reduces. The fatty acids composition of the leaves and rhizomes of Iris sibirica was established for the first time.Key words: Iris sibirica fatty acids acyl-lipid desaturases gas chromatography-mass spectrometry.