Phase equilibrium of Pb-Au and Pb-Sn systems in vacuum distillation have been predicted based on molecular interaction volume model (MIVM). A significant advantage of the model lies in its ability to predict the thermodynamic properties of liquid alloys using only binary infinite activity coefficients. The calculated activity coefficients are compared with experimental data showing good agreement with each other. This shows that the prediction effect of the proposed method is of better stability and reliability because the MIVM has a good physical basis. Crown Copyright (c) 2011 Published by Elsevier B.V. All rights reserved.