Liquid-liquid phase separation is undesirable in crystallization as it leads to slow crystal growth and uncontrollable crystal morphology. Therefore, it is necessary to identify the conditions under which liquid-liquid phase split occurs, so as to avoid crystallization process taking place at such conditions. In this study, an experimental approach is developed to systematically construct the solid-liquid-liquid equilibrium (SLLE) phase diagram. A four-component system is used to demonstrate the experimental technique and the overall workflow in developing an SLLE phase diagram. (c) 2007 American Institute of Chemical Engineers