The application of a synergistic solvent extraction by the formation of ternary complex with pyrocatechol violet (PV) and benzalkonium chloride (BC) was studied for determination of trace Zn(II) in water samples. The pH of sample solution and the amount of PV and BC added were optimized for the formation of the stable complex, a proper solvent was selected for the effective extraction, and the concentration of nitric acid was fixed for the back extraction of the complex from the solvent. After the ionic strength of 100 mL sample solution was adjusted to 0.1 M by adding NaCl and the pH was fixed at 9 with a carbonate buffer, 1.0 mL of 2% PV solution was added to form Zn(II)-PV complex then the Zn(II)-PV/BC ternary complex was made by adding 1.0 mL of 10% BC solution. The ternary complex was extracted into 10 mL of MIBK. And the ternary complex was back-extracted with 10 mL of 1.0 mol/L nitric acid to determine Zn(II) by a flame atomic absorption spectrophotometer (flame-AAS). The interference of concomitant ions on the extraction of Zn(II) was investigated. This procedure was applied to the analysis of three real samples such as Dalbang-dam water, laboratory tap water and Jungnajin seawater. The recoveries of Zn(II) in spiked samples were 86.58-104.1%.