The　relaxed　structures　and　the　formation　and　migration　energies　of　the　mono-vacancy　in　L1(2)-type　Ni3Al　ordered　alloy　have　been　investigated　by　combining　the　modified　analytical　embedded-atom　method　(MAEAM)　with　molecular　dynamics　(MD)　simulation.　The　movements　of　the　atoms　in　the　vicinity　of　the　mono-vacancy　are　toward　the　vacancy,　except　for　the　second-nearest-neighbor　Al　atoms　and　the　fifth-nearest-neighbor　Ni　atoms　around　an　Al　vacancy　and　the　third-nearest-neighbor　All　atoms　and　the　fourth-nearest-neighbor　Ni　atoms　around　a　Ni　vacancy　that　move　outward　from　the　vacancy.　Furthermore,　each　of　the　atoms　in　the　vicinity　of　either　an　Al　or　a　Ni　vacancy　moves　approximately　along　a　line　connected　between　the　atom　and　the　vacancy.　From　energy　minimization,　it　is　easy　for　a　Ni　vacancy　to　form　and　to　migrate　in　one　nearest-neighbor　jump.　(C)　2008　Elsevier　Ltd.　All　rights　reserved.