As-Selective　Laser　Melted　(as-SLMed)　Ti6Al4V　in　horizontal　direction　possess　poor　ductility　because　of　acicular　alpha＇　martensite　and　columnar　beta　grains　in　microstructure.　However,　traditional　ductility　improvement　methods　including　high-temperature　preheating　or　heat　treatment　will　decrease　not　only　strength　but　also　the　efficiency　of　SLM　fabrication　to　application.　For　a　satisfactory　mechanical　property　of　as-SLMed　Ti6Al4V　alloy,　some　special　temperature　evolution　conditions　brought　about　from　processing　parameters　such　as　layer　thickness,　hatch　spacing,　energy　density　and　area　ratios　between　support　structure　and　part,　were　carried　out　in　the　paper.　Scanning　electron　microscopy　(SEM)　and　X-ray　diffraction　(XRD)　were　used　to　characterize　the　microstructure.　The　microstructure　of　as-SLMed　specimens　are　found　to　be　different　extent　decomposing　of　alpha＇　martensite.　Also,　the　formation　mechanisms　of　such　microstructural　variables　are　proposed　based　on　temperature　evolution　vs　time　during　SLM　process.　Moreover,　the　tensile　test　presents　high　elongation　(＞8%)　is　achieved　for　horizontally　as-SLMed　Ti6Al4V　specimens　without　lowering　their　strength　(the　ultimate　tensile　strength　similar　to　1260　+/-　30　MPa　and　yield　strength　similar　to　1160　+/-　50　-　MPa),　which　markedly　exceed　ASTM　standard　for　castings.　The　mechanical　proper-　ties　and　fracture　mechanisms　of　specimens　are　obviously　affected　by　the　width　of　alpha＇/alpha　martensite　and　the　content　of　beta　phase.　This　work　marks　an　important　step　forward　in　the　understanding　of　microstructural　tailoring　in　SLM　process　for　a　high-performance　Ti6Al4V　alloy.　(C)　2019　Elsevier　B.V.　All　rights　reserved.