The objective of this work is to develop a predictive dynamical model of a nanoencapsulation process using an emulsion diffusion method. This inodel describes the formation of the polymeric membrane around the oil droplet and its size reduction due to the solvent diffusion. To this end, we assume that the phase separation is only due to purrely diffusive mechanism. This work is illustrated on the formation of poly-epsilon-caprolactone (PCL) around the oily core formed of labrafac from the initial homogeneous polymer-solvent-nonsolvent solution (PCL. ethyl acetate, and labrafac). The polymeric membrane formation, the size reduction of the nanocapsule after the solvent diffusion. and the morphology of nanocapsules are experimentally investigated. It is shown that the results obtained in simulation from the dynamical model are in agreement with the experimental ones. The model is then used to predict the effect of the initial composition on the nanocapsule morphology. (C) 2009 American Institute of Chemical Engineers AIChE J, 55: 2094-2105, 2009