In the paper studies were presented related to application of CYANEX 272 (di(2,4,4- trimethylpentyl)phosphine acid) extractant in the extractive separation of nickel(II) and cobalt(II) ions originating from a sulphate solution. Values of pH_0.5 amounted to 4.6 and 5.7 for cobalt(II) and nickel(II) ions, respectively, which permitted selective separation of the ions. Simulation of the three- stage extraction process, performed in laboratory conditions, permitted to conclude that such a process allows for a selective separation of cobalt(II) and nickel(II) ions although it requires appropriate modification only when pH of the aqueous phase is controlled.