Thermal cycling tests of repeated melting/freezing processes were performed to check the thermal stability of Mg-25Al-15Zn-14 Cu alloy as phase change thermal storage material(PCM). Latent heat storage capacity and phase transition temperature of the PCMs were determined by differential scanning calorimetry(DSC) technique as a function of repeated thermal cycles such as 0, 100, 200, and 1000. The present work also comprised the investigation of the density and microstructure of Mg-25Al-15Zn-14 Cu alloy before and after thermal cycles by using the hydrostatic method and optical microscopy(OM), X-ray diffraction(XRD), and electron probe microanalysis(EPMA), respectively. The results show that the melting temperature of alloy after 1000 thermal cycles is 415.1 ℃ and the latent heat value is 190.4 J/g. Compared with the original alloy, the phase transition temperature will increase by 1.87% and the value of phase change latent heat will decrease by 7.35%, which are in a suitable range. Therefore, Mg-25Al-15Zn-14 Cu alloy has a good thermal reliability in terms of the change in its thermal properties with respect to thermal cycling for 1000, and can be used for a middle-temperature thermal storage utility. Thermal cycling tests of repeated melting / freezing processes were performed to check the thermal stability of Mg-25Al-15Zn-14 Cu alloys as phase change thermal storage material (PCM). Latent heat storage capacity and phase transition temperature of the PCMs were determined by Differential scanning calorimetry (DSC) technique as a function of repeated thermal cycles such as 0, 100, 200, and 1000. The present work also constituted the investigation of the density and microstructure of Mg-25Al-15Zn-14 Cu alloy before and after thermal cycles by using the hydrostatic method and optical microscopy (OM), X-ray diffraction (XRD), and electron probe microanalysis (EPMA), respectively. The results show that the melting temperature of alloy after 1000 thermal cycles is 415.1 ° C and the The latent heat value is 190.4 J / g. Compared with the original alloy, the phase transition temperature will increase by 1.87% and the value of phase change latent heat will decrease by 7.35%, which are in a suitable range. T herefore, Mg-25Al-15Zn-14 Cu alloy has a good thermal reliability in terms of the change in its thermal properties with respect to thermal cycling for 1000, and can be used for a middle-temperature thermal storage utility.