Laser　micro-welding　differs　from　macro-welding　in　that　at　least　one　dimension　of　the　weld　is　less　than　100　mu　m.　Although　process　research　on　laser　micro-welding　has　recently　made　some　progress,　the　influence　of　welding　mode　on　microstructure　and　corrosion　resistance　has　remained　unknown,　which　has　been　shown　to　have　a　significant　influence　on　laser　macro-welding.　In　this　work,　a　single-mode　fiber　laser　equipped　with　a　scanning　galvanometer　is　used　to　weld　AISI304　stainless　steel　foils　with　a　thickness　of　100　mu　m.　Similar　to　laser　macro　-welding,　keyhole　formation　is　used　to　describe　two　welding　modes,　namely　thermal　conduction　welding　and　penetration　welding.　The　laser-material　interaction　experiences　a　transient　phase　in　which　the　welding　mode　alternates　between　conduction　welding　and　penetration　welding　as　reported　by　previous　work.　However,　we　show　that　gas　protection　eliminates　the　transient　phase,　proving　that　the　transient　phase　develops　as　a　result　of　the　unsteadiness　of　the　penetration　welding　caused　by　oxidation　during　the　welding　process.　The　crystallographic　texture　and　phase　constitution　vary　between　conduction　and　penetration　welds　due　to　variations　in　heat　transfer　behavior　during　welding.　The　conduction　weld　has　greater　sigma　3　CSL　boundaries　and　a　more　uniform　micro-structure　than　the　penetration　weld,　resulting　in　better　corrosion　resistance.