Abstract <p>This paper presents the results of a study of the composition and content of lipids and fatty acids (FA) in soft tissues of invasive mollusks of the genus <i>Dreissena</i> inhabiting the Kuybyshev Reservoir. An identical composition of phospholipids (PL) and neutral lipids (NL) in bodies, mantle tissues, liver, and gills were found in the species <i>D. polymorpha</i> and <i>D. bugensis</i> occurring in different parts of the reservoir. Phosphatidylcholine (PC) and phosphatidylethanolamine (PEA) predominate in the PL structure with PC in the gills of <i>D. polymorpha</i> quantitatively exceeding PEA in the other organs. Among the NLs, cholesterol (CH) and triacylglycerides (TAG) dominate. High concentrations of fat in liver and whole individuals of both species indicate favorable habitat conditions in the areas studied. The FA profile of the mollusks is approximately the same; the most significant acids in the liver are palmitic acid, eicosenoic acid, eicosapentaenoic acid, and docosapentaenoic acid. <i>D. polymorpha</i> shows a predominance of polyunsaturated FA, whereas <i>D. bugensis</i> shows a predominance of monounsaturated FA.</p>