Fatigue　crack　growth　behaviours　in　different　welding　zones　of　laser　beam　welded　specimens　were　investigated　using　central　crack　tension　specimens　for　6156　aluminium　alloy　under　constant　amplitude　loading　at　nominal　applied　stress　ratio　R　=　0.5,　0.06,　-1.　The　experimental　results　showed　that　base　metal　(BM)　exhibited　superior　fatigue　crack　resistance　compared　to　weldmetal　(WM)　and　heat-affected　zone　(HAZ).　Crack　growth　resistance　of　WM　was　the　lowest.　The　exponent　m　values　for　BM　and　HAZ　at　different　stress　ratios　are　close　and　around　2.6,　while　m　for　WM　at　different　stress　ratio　is　around　4.7.　The　discrepancy　between　crack　growth　rates　for　WM　and　BM　is　more　evident　with　increasing　stress　ratio,　while　it　is　a　little　change　for　HAZ　and　BM.　Change　of　the　microstructure　in　WM　deteriorates　the　resistance　of　fatigue　crack　growth　compared　to　BM.　It　was　mainly　due　to　grain　boundary　liquation　and　dissolving　of　second-phase　particles　in　the　weld　region.　It　was　also　found　that　the　variety　of　fatigue　crack　resistance　for　different　welding　zones　is　in　conformity　with　the　change　of　hardness.　BM　with　the　highest　hardness　exhibited　the　maximum　resistance　for　fatigue　crack,　and　WM　with　the　lowest　hardness　exhibited　the　minimum　fatigue　crack　resistance.