To provide a method for casting a magnesium alloy ingot, which has no defect and can be surely obtained, and further to provide a casting mold used for the method.

In the method for casting the magnesium alloy ingot, molten metal L and solidified portions surrounding the molten metal are compressed in the horizontal direction, when the ingot is casted by pouring the molten metal L of the magnesium alloy into a cavity 5 opened upward in a casting mold 1. The casting mold 1 for casting the magnesium alloy ingot comprises a bottom wall 2, a pair of fixed walls 3a, 3b uprightly rising from the bottom wall 2 so as to face to each other, and a pair of side walls 4a, 4b which slide on the bottom wall 2 so as to approach to and separate from each other between the fixed walls 3a, 3b.