N-ethyl-2-aminocyclopentene-1-dithiocarboxylic acid is an excellent synthetic carrier for highly efficient and selective transport of Cu(II) ions through a liquid membrane and has the ability to transport Cu(II) ions uphill. In the presence of hydrazine sulfate as a reducing agent and thiocyanate as a metal ion acceptor in the receiving phase and at the optimum pH of 1.5, about 100% of copper was transported over a period of 1 h. The carrier can selectively and efficiently transport Cu(II) ion from aqueous solutions containing other cations such as Mg2+, Ca2+, Co2+, Ni2+, Cd2+, Fe2+, Cr3+, Cr6+, Zn2+, Mn2+, Pd2+, Pb2+, Hg2+, Sn2+, Fe3+. Al3+ and Ag+.