A dilute polymer solution as the organic membrane phase was used to improve emulsion stability during extraction of penicillin G in emulsion liquid membrane (ELM) systems. Viscoelastic polymers were used to prepare the dilute polymer solution, which followed behavior of a non-Newtonian fluid. The effects of composition of polymer and surfactant in the membrane phase on extraction efficiency of penicillin G were investigated at three different w/o ratios. Simultaneously, emulsion swelling and membrane breakage were observed in order to analyze the ELM system. Use of the dilute polymer solution resulted in an increase in enrichment ratio of penicillin G concentration due to improvement of emulsion stability, independent of the w/o ratio. Also, an optimal composition of the membrane phase at each w/o ratio was obtained. which seems to be useful for development of a more practical ELM system having a high enrichment ratio and degree of extraction. (C) 2004 Elsevier B.V. All rights reserved.