The extraction and concentration of phenylalanine by the continuous CSTR emulsion liquid membrane (ELM) separation process has been evaluated. We discussed the influence of operating conditions on the separation and concentration efficiencies of phenylalanine. It was found that the extraction rate of phenyl-alanine increased as the amount of emulsion used and the internal concentration of H+ increased. However, the concentration ratio of phenylalanine increased as the emulsion amount and acid concentration increased only up to a certain limit and then declined with further increases of these. The reduction of the concentration ratio is due to the swelling of the emulsion drops. Two effects, swelling owing to osmotic pressure and swelling caused by the entrainment of water due to mechanical agitation, are responsible for the swelling of emulsion drops. A mass transfer model for analyzing the extraction of phenylalanine by liquid surfactant membrane is presented. The model assumes that the extraction and stripping reactions are reversible, and that the reaction equilibrium exists in both the internal and the external interfaces. The scheme for mass transfer is based on a hollow sphere model. The phenomena of osmotic swelling, mechanical entrainment, and breakage are all considered in the mathematical treatment. The effects of operation parameters on the extraction efficiency and concentration ratio are discussed by simulation.