In this work, a self-consistent thermodynamic database for the Mg-Al-Ca-Sr system using the modified quasichemical model has been constructed. The thermodynamic description of the quaternary system was established by combining the thermodynamic descriptions of the constituent binary and ternary sub-systems. The Mg-Al-Ca and Mg-Al-Sr systems were investigated by combining thermodynamic modeling and experimental investigation. The experimental investigation has been performed using DSC, XRD, SEM and EPMA. Also, isothermal sections at 300°C and 400°C were constructed for the Mg-Al-Ca and Mg-Al-Sr systems. In the Mg-Al-Sr system, six ternary solubilities of the binary compounds extended into the ternary system have been found and denoted as (Mg 17 Sr 2 ), (Mg 23 Sr 6 ), (Mg 38 Sr 9 ), (Mg 2 Sr), (Al 4 Sr) and (Al 2 Sr). The reported ternary compound in the literature (Mg 58 Al 38 Sr 4 ) has been observed in this work. In the Mg-Al-Ca system, three binary compounds were found to dissolve the third component in the ternary system and were denoted as (Al 2 Ca), (Al 3 Ca 8 ), and (Mg 2 Ca). The ternary compound (C36) reported in the literature has been confirmed.  A comparison between the calculated liquidus projection of the Mg-Ca-Sr system using the modified quasichemical model and random solution model has been presented. It was found that while the random solution model agrees well with the experimental phase diagram, the modified quasichemical model gives better agreement with the experimental thermodynamic data and the experimental phase diagram.  Liquidus projection of the Al-Ca-Sr system was calculated using the modified quasichemical model and combined with the other three ternaries in one database for the Mg-Al-Ca-Sr system.