The extraction of zirconium(VI) from an aqueous solution of constant ionic strength with versatic acid - 10 dissolved in benzene was studied as a function of pH and the concentration of zirconium(VI) and organic acid. The effects of sulphate and chlorine ions on the extraction of the zirconium(VI) ware briefly examined. It was revealed that (ZrOR₂.2RH) is the predominant species of extracted zirconium(VI) in the versatic acid - 10. The chemical equation and the apparent equilibrium constants thereof have been determined as follows. (ZrO^(2+))aq＋2(R₂H₂)_(org) = (ZrOR₂.2RH)_(org)＋2(H^+)_(aq) Kzr = (ZrOR₂.2RH)_(org)·(H^+)²/(ZrO^(2+))_(aq)·(R₂H₂)²_(org)＝3.3×10^(-7) The synergistic effects of TBP and D2EHPA were also studied. In the mixed solvent with 0.1M TBP, the synergistic effect was observed, while the mixed solvent with D2EHPA showed the anti-synergistic effect.