CO2　laser　beam　was　used　to　weld　2519-T87　high　strength　aluminum　alloy,　and　the　microstructure　and　mechanical　properties　of　the　welds　were　studied　and　compared　with　the　melting　electrode　inert　gas　(MIG)　welds.　Results　indicate　that　the　grains　in　laser　welds　are　very　fine,　and　the　eutectic　phase　distributes　more　uniformly.　After　aging　treatment,　there　are　lots　of　finer　θ′　phase　in　laser　welds.　And　there　is　no　equiaxed　grain　zone　along　the　laser　weld　fusion　line.　Whereas　the　grains　in　MIG　welds　are　coarser.　The　eutectic　phase　is　strip　morphology　and　network　distributes　along　the　grain　boundary.　After　aging　treatment,　the　size　of　θ′　phase　is　big　and　number　of　θ′　phase　is　small,　and　it　does　not　distribute　uniformly　in　the　grains.　There　is　a　wide　equiaxed　grain　zone　along　the　fusion　line.　The　tensile　strength　of　the　laser　weld　after　aging　treatment　can　reach　74%　of　that　of　the　base　metal,　whereas　the　tensile　strength　of　MIG　weld　is　only　61%　of　that　of　the　base　metal.　And　there　is　no　softened　zone　in　the　heat　affected　zone　(HAZ)　of　laser　welds.