In this study, terminal modified poly(ethylene glycerol) (PEG) was employed as the phase-forming polymer to construct aqueous two-phase (ATP). After the phase equilibrium, 95.8% penicillin could be extracted into imidazole-terminal PEG-rich phase efficiently. Imidazole-terminal PEG (I-PEG) was separated from the aqueous phase containing penicillin to hydrophobic ionic liquid phase at basic pH, and a weak acidic aqueous phase was then employed to recover the I-PEG from the hydrophobic ionic liquid phase into water at pH 5.5-6. The recycle of the polymer was achieved with the aid of hydrophobic ionic liquids. (C) 2008 Elsevier B.V. All rights reserved.