The extraction of U(VI), Sr, and Cs from solutions of mineral acids (HNO 3 , HCl) with a crown ether, cis-syn-cis-dicyclohexyl-18-crown-6 (DCH18C6-А), dissolved in ionic liquids (ILs), 1-butyl-3-methylimidazolium derivatives (bmimPF 6 , bmimBF 4 , bmimTf 2 N), was studied. The best physicochemical characteristics (solubility in the aqueous phase, viscosity, hydrophobicity, etc.) are exhibited by a solution of DCH18C6-A in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (bmimTf 2 N). The metal distribution ratios (D М ) in the extraction with a 0.01 M DCH18C6-А solution are 80 for CsNO 3 , 78 for CsCl, and 162 for Sr(NO 3 ) 2 . With an increase in the HNO 3 and HCl concentrations, D М decreases, and with 1 M acids it does not exceed 1. The U(VI) extraction from nitric acid solutions with a 1 M solution of DCH18C6-А in bmimTf 2 N initially increases with an increase in the aqueous phase acidity, with D U(VI) reaching 5.4 in 4 M HNO 3 , but then decreases in the interval 4-8 M HNO 3 , whereas in the extraction with a 1 M solution of tributyl phosphate (TBP) in bmimTf 2 N D U(VI) monotonically increases with an increase in the HNO 3 concentration to 8 M. From hydrochloric acid solutions, U(VI) is extracted with solutions of DCH18C6-А in bmimTf 2 N with the D U(VI) values characteristic of solutions of DCH18C6-А in nonpolar organic diluents. On the whole, ILs as solvents exhibit unusual properties in the extraction of alkali and alkaline-earth elements from neutral solutions and of U(VI) with TBP from concentrated nitric acid solutions.In liquid-liquid extraction, organic solvents strongly affect the distribution ratios of metals recovered from the aqueous phase (D М ). The solvent effect is particularly pronounced in the extraction of metal salts with crown ethers (CEs). In these systems, the range of D М variation in various solvents can reach 10 6 [1]. In such systems, the solvent not only acts as a diluent for the extractants, but also actively participates in the formation of complexes in the organic phase. Proceeding with studies in this field, we examined the role of the solvent in the crown ether-ionic liquid (IL) systems in the extraction of U(VI), Sr, and Cs from mineral acid solutions.Hydrophobic functionalized CEs are widely used as selective extractants in recovery and separation of various metal ions, including ions of radioactive metals [2]. It was found that the heterogeneous interactions between the aqueous and organic phases in CEcontaining systems can occur by different mechanisms depending on the type and concentration of inorganic acid and on the structure of the organic solvent used [3]. Possible alternatives to the examined solvents are ILs, which are low-melting derivatives of quaternary ammonium salts [4]. These are nonflammable, nonvolatile, thermally stable, and weakly toxic compounds ionized in the liquid state and excellently conducting electric current. This fact facilitates the transfer of metal salts in the form of ion pairs from the aqueous phase into solutions of CEs in...