Abstract: A method for manufacturing a composite metal alloy. An Mg material as an alloy base material and a carbon nanomaterial are mixed together to obtain a mixture in which the Mg material is covered with particles of the carbon nanomaterial. The mixture of the Mg material and carbon nanomaterial are sintered to obtain an Mg sintered compact including the carbon nanomaterial. The Mg sintered compact including the carbon nanomaterial is dissolved to obtain a melt of the composite metal alloy.