Separation of cobalt(II) and nickel(II) by using a hydroxyoxime extractant has been investigated both in liquid-liquid extraction and in a liquid surfactant membrane (LSM) system. In the liquid-liquid equilibrium extraction studies, hydroxyoximes showed significant extractability for nickel ions, although LIX 84 was found to have exceptional chelating affinity for nickel ions. In the LSM system functionalized by hydroxyoxime, the cobalt ions were efficiently separated from nickel ions as a result of slower permeation of nickel chelates across the emulsion membrane. More complete cobalt recovery was achieved in the LSMs dosed with LM 860 than when the same carrier was applied to the liquid-liquid extraction system. Furthermore, cobalt permeation rate was enhanced threefold when a quaternary ammonium type of cationic surfactant was used as an emulsifier due to carrier interaction with surfactant at the reaction interface. The permeation mechanism of ions in LSMs was elucidated by an interfacial reaction model which took into account the adsorption of the carrier and surfactant at the reaction interface.