Recently, Mg-Zn-Ca ternary system has been reported to have excellent creep resistance since addition of Ca form Mg2Ca with high thermal stability and addition of Zn induces solution hardening effect. However, complete thermodynamic study has not besn performed yet. In this study, phase equilibrium and thermodynamic study about Mg-Zn-Ca system including 2 ternary compounds (τ1: Ca2Mg6Zn3, τ2; Ca1Mg3Zn6) has been considered. In order to assess thermodynamic parameters of ternary compound τ2, isothermal section and isopleths has been made by using DSC, DTA, XRD, SEM and TEM around the composition range of τ2. Calculated phase diagram of Mg-Zn-Ca ternary system has been studied with assessed ternary compound parameters. Solidification simulation via Scheil equation has been discussed with as-casted specimens and after heat treatment, and in particular invariant reactions have been compared with bulk glass form region.