DEHPA in petrofin has been used for the extractive separation of La(III) and Ni(II) from a feed solution containing 1.389 g L-1 La(III) and 1.760 g L-1 Ni(II) using a complexing agent, lactic acid. Various experiments have been performed taking into account the effect of different operating parameters such as equilibration time, pH, concentrations of lactic acid and DEHPA, organic to aqueous phase volume ratio, temperature, and diluents. Very high separation factors have been obtained under several experimental conditions due to complete separation of La(III) from Ni(II). Separation factor (II) obtained for the extraction of 1.389 g L-1 La(III) and 1.76 g L-1 Ni(II) at initial pH 4.3 using 0.1 M lactic acid with 0.2 M DEHPA in petrofin was 3827.8. A maximum of 99.8% of La (III) could be stripped off the loaded organic phase with 1.2 M HCI and stripping of Ni(II) was not possible. No significant changes have been observed in the extraction ability of DEHPA as evident from regeneration studies. The presence of commonly associated rare earths (Ce(III), Nd(III), Pr(III), Y(III)) has not shown any adverse effect on the separation of La(III) and Ni(II). (C) 2017 Elsevier B.V. All rights reserved.