In the present study, the high temperature mechanical properties and creep resistance of Mg-Zn-Y-Ca alloys has been investigated. The Mg-4Zn-0.8Y alloy consists of ${alpha}$-Mg matrix and icosahedral quasicrystalline phase. Calcium addition into Mg-4n-0.8Y based alloy results in the formation of ${ au}(Ca_{2}Mg_{6}Zn_{3})$ and $Mg_{2}Ca$ as the second solidification phases. Creep properties of the Mg-Zn-Y and Mg-Zn-Ca based alloys measured at applied stresses between 65 MPa and 85 MPa are significantly improved with adding calcium and yttrium, respectively. The improved creep resistance is due to the formation of thermally stable $Mg_{2}Ca$ phase.