The present study focuses on investigating the tensile mechanical properties and failure behaviours of the LAZ1021 Mg-Li alloy. The tensile tests of LAZ1021 specimens were performed at-25°C to 250°C, with a tensile strain rate of 1.67 × l0-3/s. The XRD analysis results suggested that the microstructural characteristics of LAZ1021 were combined with the Mg-rich α-phase and the Li-rich P-phase, and there was less phase composition change after tensile tests at various testing temperatures. The tensile strength and elongations were sensitive to the deformation temperatures. The total elongation was significantly increased from 4% at-25°C to about 55% above 100°C tensile testing temperatures. A significant ductile-to-brittle transition temperature (DBTT) was recognized at about 50°C. The failures, which occurred from brittle fracture with evident cleavage to ductile dimpled ruptures, is related to the transition of slip systems with increasing temperatures and the cavitation between α/β-phase interface.