Solvent extraction of nickel(II) and uranium(VI) was studied with 3-methyl-4-(p-nitrobenzoyl)-5-oxo-phenylprazole(HNP) dissolved in benzene. The formation and distribution constants for U(VI) and Ni(II) were calculated from extraction data and both are higher for U(VI) than Ni(II). None of the metals was adequately extracted in the absence of a synergist. However, synergic enhancement in extraction was observed in the presence of tributyl phosphate(TBP). Separation procedures for U(VI) and Ni(II) by adjustment of the conditions of the aqueous phase are presented. Complexing agents such as EDTA, oxalate and citrate anions adversely affected the extraction of these metals.