Results of the comparative thermodynamic study of the Pb-Bi2Mg3 system, obtained experimentally by Oelsen calorimetry and calculated by different predicting methods (general solution model, Toop, Hillert, Kohler, Muggianu) are given in this paper. Corresponding analytical expressions for the lead partial molar thermodynamic quantities were obtained by using Krupkowski method and Margules power series, comparatively. The phase diagram of the investigated system is also presented.