Knowledge of the phase equilibria of Mg-alloy systems is crucial for improving existing alloys and developing new ones. Besides, processing of materials depends strongly on accurate thermodynamic data of the material system. By thermodynamic modeling a set of optimized model parameters of the ternary Mg-Al-Ca and Mg-Al-Sb systems are obtained by considering the experimental phase equilibria and thermodynamic data available in the literature. The calculated sub-binary diagrams agree well with the experimental data from the literature. Also, The phase diagram of Mg-Al-Sr and Mg-Al-Ca systems were investigated experimentally by differential scanning calorimeter (DSC). The experimental work focused on the critical regions after reviewing the phase diagrams developed by thermodynamics and experimental results. DSC results provided information on the following thermophysical properties: onset temperature, melting enthalpy and liquidus temperatures. Comparison between these results and thermodynamic findings will be discussed. These results along with x-ray diffraction analysis will be used later to establish the equilibria in Mg-Al-Sr and Mg-Al-Ca systems.