Methyl linolenate was separated from its analogues by a new extraction system constructed by solvent, imidazolium based ionic liquids and cuprous salt. Firstly, the effect of ionic liquid on the dissolution of CuCl in acetonitrile, N,N-dimethylformamide (DMF), methanol and water was evaluated by visual observation. [C(4)Mim][Cl] can improve the dissolution of CuCl in acetonitrile. Then, for the new system as acetonitrile-ILs-CuCl, extraction equilibrium, distribution ratio and selectivity of methyl linolenate and its analogues were determined by gas chromatography analysis and the mass balance. The extraction time, IL structures and CuCl concentrations were investigated. Distribution ratio decreased slightly, but selectivity increased significantly with the addition of CuCl, [C(4)Mim][Cl] or [C(4)Vim][NTF2] into acetonitrile. [C(4)Vim][NTF2] had higher selectivity than [C(4)Mim][Cl]. But the selectivity of the system combining CuCl with [C(4)Vim][NTF2] was much lower than with [C(4)Mim][Cl]. For the CuCl-[C(4)Mim][Cl]-acetonitrile, the extraction efficiency was better than CuCl-acetonitrile, increasing Cu+ concentration effectively improved the separation selectivity when ratio of CuCl/[C(4)Mim][Cl] was less than 1. Compared with previous aqueous AgNO3 extractions, the method of using CuCl is a much cheaper and practical way to enrich unsaturated fatty acid. (C) 2018 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.