Abstract: A 1.5 mm-thick Mg-8.4wt%Li alloy sheet was obtained through warm-rolling at 473 K with a total reduction of 92.5% after melting, casting, ingot homogenization annealing at 573 K for 24 h. A percentage elongation up to 500% was demonstrated for such sheet at 473 K and initial strain rate of 1.67 × 10^-3/sec after said 1.5 mm sheet passed the recrystallized salt bath annealing. The strain rate sensitivity index was 0.47 through phenomenological calculation, indicating that grain boundary sliding is the dominant deformation mechanism. The microstructure of such sheet after 573 K × 1 h salt bath annealing and superplastic deformation was studied by TEM and optical microscope. It was found that the grain size after salt bath annealing was 2.4 μm and that within the gauge length of specimen after superplastic deformation was 5.8 μm, indicating the occurrence of certain grain growth which is relevant to the atomic diffusion mechanism. SEM was used to examine the fractograph of specimen after superplastic deformation. It was found that the dimples are fine, deep and roundly distributed, thus retaining the original feature of equiaxial grains.