Abstract: The present invention provides a magnesium-based composite material that can achieve excellent performance such as high tensile strength not only at ordinary temperature but also at high temperature. The magnesium-based composite material of the present invention is Al2Ca-containing magnesium-based composite material, wherein said composite material is obtained by a solid-phase reaction of an aluminum-containing magnesium alloy and an additive, said additive being calcium oxide, and said composite material contains Al2Ca formed in the solid-phase reaction. In the magnesium-based composite material, CaO, in combination with Al2Ca, can be dispersed.