A method of manufacturing a magnetic memory device may include forming a lower magnetic layer, a tunnel barrier layer, and an upper magnetic layer on a substrate, forming a magnetic tunnel junction pattern by etching a stacked structure including the lower magnetic layer, the tunnel barrier layer, and the upper magnetic layer, forming a boron-absorption layer covering the magnetic tunnel junction pattern, and performing a heat treatment process so that boron included in the upper and lower magnetic layers may be absorbed by the boron-absorption layer. The heat treatment process may be undertaken in a gaseous atmosphere including at least one of hydrogen, oxygen, and nitrogen.