We have conducted solvent extraction experiments of FeCl₃ in HCl solution with Alamine336 as an extractant. Solvent extraction reaction depended on the ratio of initial concentration of Alamine336 to FeCl₃. When the concentration of Alamine336 was in excess to that of FeCl₃, the extractant reacted as a dimer. When the initial concentration ratio of Alamine336 to FeCl₃ was below three, ferric chloride was extracted by monomeric extractant. The equilibrium constants of solvent extraction were determined by applying ionic equilibria to the experimental data. These ionic equilibria consisted of chemical equilibria, mass and charge balance equations. The activity coefficients of solutes in aqueous phase were calculated by using Bromley equation. The predicted distribution coefficients of iron agreed well with those measured.