ABSTRACT The objective of this work is the evaluation of the separation/concentration of L-phenylalanine by means of nondispersive extraction and backextraction in hollow fiber modules and the determination of the equilibrium and kinetic parameters, which will allow the description of the separation process. An organic solution based on Aliquat 336, 30% (v/v); isodecanol, 30% (v/v); and kerosene is used as a selective extraction medium. The extraction of L-phenylalanine takes place at pH 10·5, and the backextraction takes place at pH 0·5, with a sulfuric acid solution. The nondispersive extraction and backextraction process for the separation/con-centration of L-phenylalanine is described by means of a mathematical model based on seven differential equations. Its resolution is performed by the gPROMS simulation package after introduction of the chemical equilibrium extraction parameters KqE = 1·32 and K1 = 1·25 × 10−3 allowing calculation of the optimum value of the mass transfer coefficient, KM = 1·12 × 10−8 m/s, which is in the range of previously reported values. This model and its parameters are useful for establishing the viability of the industrial separation/concentration processes of L-phenylalanine. Keywords:: L-PhenylalanineHollow fiberNondispersive extraction and backextraction