Two-aqueous phase extraction of phenol and benzyl alcohol as a solute from their aqueous solutions was investigated using polyethoxylated alcohols (CiEj) as a biodegradable non-ionic surfactant. First, the phase diagrams of the binary systems, water-surfactant (Oxo-C10E3 and OxoC(13)E(9)), and the pseudo-binary systems, water-surfactant with a constant concentration of solute was determined. The effect of sodium chloride and sodium sulphate on water-surfactant systems were studied. According to the given surfactants concentrations and temperatures, the extraction results were expressed by the following four parameters, percentage of extracted solute, E, which reached 95 and 90% for phenol and benzyl alcohol, respectively, residual concentrations of solute, X-sw,X- and the surfactant, X-t,X-w, in the dilute phase and volume fraction of the coacervate at the equilibrium condition, phi(c). The values of these parameters were determined by an analyzing central composite designs. After the first extraction process, phenol and benzyl alcohol concentrations in the effluent were reduced about ten times for the first and four times for the second, correspondingly. (C) 2005 Elsevier B.V. All rights reserved.