Ti-6Al-4V　alloys　mad　by　additive　manufacturing　(AM)　with　slower　cooling　rate　(e.　g.,　direct　energy　deposition　(DED))　generally　have　the　problem　of　severe　coarsening　of　α　phase.　This　study　presents　a　method　to　refine　the　microstructure　of　the　primary　β　phase　formed　during　the　solid–liquid　transformation,　microstructures　formed　during　the　β　→　α　+　β　transformation,　and　recrystallized　microstructures　formed　during　the　repeated　heating　cycles　encountered　in　AM　processes.　This　is　accomplished　by　the　in　situ　precipitation　of　nano-sized　dispersed　high-melting-point　yttria　Y2O3　particles.　The　addition　of　micron-sized　particles　with　high　melting　points　can　refine　primary　crystallized　grains　and　transformed　grains　corresponding　to　the　secondary　phase　in　Ti-6Al-4V　alloys.　In　addition,　they　can　effectively　inhibit　the　recrystallization　and　growth　of　prior-deposited　metal　grains.　The　microstructural　and　tensile　properties　of　laser　additive　manufactured　with　filler　wire　Ti-6Al-4V　components　with　different　amounts　of　Y2O3　(0,　0.12,　and　0.22　wt%)　were　investigated.　The　refining　effect　of　Y2O3　was　significant　and　the　tensile　strength　of　Ti-6Al-4V　containing　0.22　wt%　Y2O3　in　the　longitudinal　and　transverse　directions　was　greater　than　that　of　Ti-6Al-4V　by　approximately　12%　and　9%,　respectively.　Concurrently,　there　was　no　loss　in　the　elongation　of　the　material　in　either　direction.　The　strategy　of　using　micron-sized　refractory　particles　to　control　phase　transformation　(primary　crystallization,　solid-state　phase　transformation,　and　recrystallization)　can　be　applied　to　the　AM　of　different　metals,　in　which　microstructures　are　susceptible　to　coarsening.　©　2021