Microstructure　of　welding　joints　in　TC4　alloy　manufactured　by　laser　processing　was　investigated　by　optical　microscope　and　scanning　electron　microscopy.　The　microhardness　from　weld　center　of　the　joint　to　base　metal　was　measured.　The　results　show　that,　in　the　base　metal,　the　microstructure　is　consisted　of　α　phase　and　dispersed　granular　β.　Microstructure　of　the　welding　joint　is　composed　of　coarse　equiaxed　zone,　columnar　grain　zone,　fine　equiaxed　zone　and　reheat　microstructure.　The　structure　in　the　coarse　equiaxed　zone　is　consisted　of　platelet　α+β,　widmanstatten　structure　α　and　basket　weave　α+β,　which　microhardness　is　lower　than　that　of　the　columnar　grain　zone　and　fine　equiaxed　zone,　but　higher　than　the　base　metal.　The　structure　in　the　columnar　grain　zone　and　fine　equiaxed　zone　is　mainly　needle-shaped　martensite.　The　microhardness　of　the　columnar　grain　is　the　highest　in　the　joint.　The　microhardness　of　HAZ　is　close　to　that　of　base　metal.