The　T-joints　of　Ti-6Al-4V　alloy　are　fabricated　by　double-sided　synchronized　laser　beam　welding　with　the　homologous　filler　wire.　The　influence　of　the　welding　conditions　on　weld　defects　such　as　lack　of　fusion　and　porosity　are　investigated.　Results　show　that　the　lack　of　fusion　defects　are　determined　by　the　laser　power,　welding　speed,　laser　incident　angle　and　position.　With　larger　enough　welding　heat　input　(higher　laser　power,　and　slower　welding　speed),　the　lower　laser　incident　angle　and　higher　laser　incident　position　are　required　to　avoid　the　lack　of　fusion　defects.　The　quantity　of　plasma/metal　vapor　above　the　molten　pool　for　weld　seam　with　the　lack　of　fusion　defects　is　larger　than　that　of　the　weld　seam　without　the　defects　under　a　certain　laser　power.　The　porosity　defects　in　the　welded　T-joints　are　mainly　the　type　of　keyhole　porosity　defects　under　different　welding　conditions,　and　the　higher　welding　speed　is　helpful　to　decrease　the　porosity　defects　under　a　certain　laser　power.　©　2016,　Chinese　Laser　Press.　All　right　reserved.