Modeling of extraction operations for caprolactam requires an accurate description of the phase compositions and the physical properties of all liquid phases. Therefore experimental liquid-liquid equilibrium data were measured for the systems water (1) + caprolactam (2) + ammonium sulfate (3) + organic solvent (4) at 293 K, 313 K, and 333 K, where the organic solvent was either benzene or toluene. Furthermore, the physical properties, density and viscosity of the separate phases and the interfacial tension of the two-phase systems, were determined. The equilibrium phase composition data were correlated using the nonrandom two-liquid model. Density data were fitted via the concentration influence of the solutes and the thermal expansion coefficient. Viscosity data were correlated using the Dole-Jones equation for describing the influence of the solute concentration and the Guzman-Andrade equation for describing the influence of temperature. Interfacial tension data were described using the Szyzkowski and the Jasper equation for describing the influence of solute concentration and temperature. Excellent agreement was found between the measured data and developed correlations.