To Supply biodiesel with the quality levels required by the standards for alternative fuels, the separation and Purification units are extremely important in the biodiesel production plants. The correct knowledge and description of the phase equilibria in systems composed by transesterification products is essential for it correct operation and Optimization of the purification process. For that purpose, the cubic-plus-association equation of state (CPA EoS) was here applied to model the phase equilibria of multicomponent systems common to biodiesel production and Purification processes. It is shown that the CPA EoS call provide a good description of the liquid-liquid equilibria of multicomponent mixtures containing alcohols, glycerol, and fatty acid esters in the temperature range of operation of the separation units ill biodiesel plants. As the liquid-liquid phase equilibrium description depends oil the EoS parameters, a discussion is also presented about the best set of parameters and the method to estimate them.