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The microstructure，tensile and damage tolerance properties in different directions of Al-Mg-Sc-Zr alloy fabricated through selective laser melting（SLM）have been investigated. The results show that the YZ plane is a bimodal grain morphology composed of fine equiaxed grains and coarse columnar grains，while the XY plane is composed of fine equiaxed grains. The yield strength and tensile strength in both 0° and 90° directions are over 500 MPa，and the anisotropy is small，while the elongation in 90° direction is significantly lower than the 0° direction due to the lack of fusion（LOF）defects between the deposited layers. The KIC of the 0° and 90° CT samples are respectively 21.41 MPa·m1/2 and 20.89 MPa·m1/2. The resistance to crack propagation in columnar grains region is lower and leading to a smaller KIC for 90° CT samples. The microstructure and defects are the two main factors that affect the anisotropy of crack propagation performance. The LOF defects play a leading role in the near-threshold regime，and the crack propagation rate is faster when the crack propagation plane is parallel to transverse direction. On the other hand，the microstructure plays a leading role in the steady-state propagation regime. The fracture surface exhibits transgranular fracture when the crack propagation plane is parallel to transverse direction，which provides higher crack propagation resistance and result in lower crack propagation rate.