Abstract:The effects of cold rolling deformation on the microstructure and mechanical properties of hot extrusion state LZ91 magnesium lithium alloy by using hardness testing, uniaxial tensile, Optical Microscopy(OM), X-ray diffraction and Scanning Electron Microscope(SEM). The results show that the hot extrusion state LZ91 magnesium lithium alloy composed by α-phase, β-phase and Mg /Zn compounds has a good plastic deformation capability, and the maximum cold rolling the is up to 95%. The alloy’s phase keeps stable during cold rolling deformation. With rolling deformation increasing, the elongation of alloy rises at first, then descends. The hardness and tensile strength have been improved alloys due to the hardening and grain refinement, and tensile strength reached 267MPa at the rolling deformation 95%.