In the supercritical antisolvent (SAS) precipitation, the thermodynamic behavior of the system influences particles morphology. However, in the case of complex multicomponent systems, thermodynamic data are limited and there is the common tendency to neglect the solutes and consider the system as pseudo-binary (solvent-CO2). Polyvinylpyrrolidone (PVP) was precipitated using SAS from acetone-ethanol mixtures and different SAS morphologies were obtained at different operating conditions. To explain the obtained morphologies, VLEs of the ternary system acetone-ethanol-CO2 and of the quaternary system PVP-acetone-ethanol-CO2 were experimentally determined using a static synthetic method. It was evident that the presence of PVP, at different concentrations in the liquid solution, had an appreciable effect on the equilibria. Once the VLEs were determined, the morphologies of the powders precipitated by SAS were justified considering the position of the corresponding operating points with respect to the PVP-acetone-ethanol-CO2 mixture critical point.