Abstract: Anew model (EVLACmodel) which can directly predict liquid activity coefficient from excess volume data are established by means of statistical thermodynamics. Anew partition function equation is developed and then V^E-x equation and γ-x equation can be derived mainly from the concepts of two liquid cell and local compositions. If V^E-x data at only one temperature are available, the isothermal γ-x data and VLE. data at different temperatures and the isobaric VLE. data at different pressures can be calculated. This method can be extended to multi-component systems without increasing any multi-component parameters.About eighty sets isothermal activity coefficients of twenty five binary systems and fifteen sets isobaric activity coefficients and VLE. data are predicted by means of this new method. Good agreements between experimental data and predicted values are obtained.