In this paper, the extraction behaviors of praseodymium(III) from an aqueous chloride- acetate medium, using 8-hydroxyquinoline (HQ), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507, HL) and their mixture, were studied, using ultraviolet-visible light (UV-vis) absorption spectroscopy. The binary equilibrium constants (log K-1, log K-2) for the complex formation PrL3 center dot 3OHL and PrQ(3) in the organic phase were determined to be - 1.98 for 2-ethylhexyl phosphonic acid mono-2-ethylbexyl ester and - 11.54 for HQ, respectively. The overall equilibrium constant (log K-12) for the ternary species PrQ(2)L(10)H(9) was estimated to be 6.01. The largest synergistic enhancement factor was calculated to be 5.39, corresponding to a HQ:P507 concentration ratio of 3:7 at pH 3.6. When P507 was added into HQ, the entire stripping could be achieved at an aqueous sulfuric acid concentration of similar to 0.02 M. In addition, for praseodymium(III) and neodymium(III), the mixture of HQ and P507 showed higher separation selectivity than HQ or P507 alone, which is important for potential industrial applications.