Aqueous two-phase system (ATPS), also called "water-in-water" emulsion, is a multi-component system (aqueous droplets dispersed in a continuous aqueous phase), formed after gently mixing two aqueous solutions of immiscible polymers. It allows the formation of different compartments without adding any organic solvent, according to a green process. Nevertheless, the kinetic stability of ATPS is generally difficult to control. Phase diagrams, which express the concentration of a polymer as a function of that of the other in solution, are used to characterise ATPS and to determine conditions for preparing emulsions from selected polymers. In this study, dextran and polyethylene oxide aqueous mixtures with different processing parameters are investigated. Phase diagrams are generated through two automatic methods (Turbiscan and LUMiSizer® technologies) and a manual one. With the diagrams obtained, it is concluded that the purity of polyethylene oxide affects the ATPS, whereas the use of polymers in powder or in solution form has no effect. In view of this result, it is allowed to prepare ATPS formulation by a simple one-step process from polymers in powder form.