Through investigating and comparing the microstructure and mechanical properties of the as-extruded Mg alloys Mg–4%Li and Mg–4%Li–6%Zn–1.2%Y(in wt%), it demonstrates that although the formation of I-phase(Mg_3Zn_6Y, icosahedral structure) could weaken the crystallographic texture and improve the mechanical strength, the mechanical anisotropy in terms of strength remains in Mg–4%Li–6%Zn–1.2%Y alloy.Failure analysis indicates that for the Mg–4%Li alloy, the fracture surfaces of the tensile samples tested along transverse direction(TD) contain a large number of plastic dimples, whereas the fracture surface exhibits quasi-cleavage characteristic when tensile samples were tested along extrusion direction(ED).For the Mg–4%Li–6%Zn–1.2%Y alloy, typical ductile fracture surfaces can be observed in both “TD” and“ED” samples. Moreover, due to the zonal distribution of broken I-phase particles, the fracture surface of “TD” samples is characterized by the typical “woody fracture”. Through investigating and comparing the microstructure and mechanical properties of the as-extruded Mg alloys Mg-4% Li and Mg-4% Li-6% Zn- 1.2% Y (in wt%), it demonstrates that although the formation of I- phase (Mg_3Zn_6Y, icosahedral structure) could weaken the crystallographic texture and improve the mechanical strength, the mechanical anisotropy in terms of strength remains in Mg-4% Li-6% Zn-1.2% Y alloy.Failure analysis indicates that for the Mg- 4% Li alloy, the fracture surfaces of the tensile samples tested along transverse direction (TD) contain a large number of plastic dimples, whereas the fracture surface exhibits quasi-cleavage characteristic when tensile samples were tested along extrusion direction (ED) .For the Typical ductile fracture surfaces can be observed in both “TD” and “ED” samples. Moreover, due to the zonal distribution of broken I-phase particles , the fracture surface of “TD ” samples is characterized by the typical “woody fracture ”.