In this work the mass transfer analysis and modeling of the hollow fiber non-dispersive liquid-liquid extraction of Cr(VI) with Aliquat 336 is reported. Experimental results corresponding to different values of the initial concentration of Cr(VI) in the aqueous phase in the range 50 g/m3 less-than-or-equal-to C0 less-than-or-equal-to 500 g/M3 Showed three different diffusional regimes depending on both the initial concentration of Cr(VI) and the linear velocities of the aqueous phase : (i) kinetic control of the mass transport in the aqueous phase, (ii) kinetic control of the mass transport through the membrane fiber wall and (iii) an intermediate region where the control is shared between the aqueous and the membrane phases. The integration of the mass conservation equation with a nonlinear equilibrium condition at the fiber wall agrees satisfactorily with the results of experiments performed at different initial concentrations of Cr(VI) and different values of the linear velocity of the aqueous phase in the range C0 greater-than-or-equal-to 50 g/m3 and 2.95 x 10(-3) m/s less-than-or-equal-to v less-than-or-equal-to 1.18 x 10(-2) m/s. An optimization of the parameters D, solute diffusivity in the aqueous phase, and K(eq), equilibrium constant of the extraction chemical reaction, with all the experimental results, using as criterion the minimum weighted standard deviation, gave as a result the value of the parameter D = 2.3 x 10(-9) m2/s and values of K(eq) dependent upon the initial concentration of Cr(VI) in the feed solution. The mass transfer model and parameters reported in this work are useful for the design and optimization of the nondispersive extraction of Cr(VI) in a hollow fiber module.