Creep rupture tests were performed for a die-cast Mg-Al-Ca alloy AX52 (X representing calcium) at 29 kinds of creep conditions in the temperature range between 423 and 498 K. The creep curve for the alloy is characterized by a minimum in the creep rate followed by an accelerating stage. The minimum creep rate (ε& m) and the creep rupture life (trup) follow the phenomenological Monkman-Grant relationship; trup = C0 /ε& m m. It is found for the AX52 die-cast alloy that the exponent m is unity and the constant C0 is 2.0 x 10-2, independent of creep testing temperature. The values of m and C0 are compared with those for another die-cast magnesium alloys. The value m=1 is generally detected for die-cast magnesium alloys. On the contrary, the value of C0 sensitively depends on alloy composition, which is reduced with increasing the concentration of alloying elements such as Al, Zn and Ca.