The reaction of zinc in chloride solution with dibutyl butylphosphonate (DBBP) in Escaid 110 has been investigated. The extraction coefficient of zinc was independent of equilibrium pH. This independence indicates that the mechanism of the extraction is a solvation. Slope analysis for the system of dilute zinc chloride solution reveals that two moles of DBBP react with one mole of zinc. A series of tests was conducted to bring DBBP to its full loading capacity, and the analysis of the results confirms this stoichiometric factor of 2 for concentrated solutions. The stoichiometric factor of water in the extraction reaction is found to be 4 by determining the activities of water and free chloride ions at various CaCl2 concentrations. The experimental data also indicate that two chloride ions are involved for each extracted zinc species.