Although electron backscatter diffraction (EBSD) analysis for Mg-Li based alloys is difficult to conduct, this technique is necessary to understand the properties of these alloys. Numerous studies have addressed the use of electron backscatter diffraction (EBSD) analysis as an effective technique for quantifying Mg-Li based alloys. However, a crystallographic orientation determination of β-Mg by EBSD has not been achieved thus far. In this study, to conduct EBSD analysis of the body-centered cubic (BCC) phase in Mg-Li based alloys with various applied equivalent strains prepared by severe plastic deformation, surface treatment techniques were established. By the use of both Ar+ ion milling and Ar+ ion etching under ultra-high vacuum conditions, the Kikuchi patterns of Mg-Li based alloys were detected. According to the results of the EBSD analysis, it was concluded that the structural evolution of BCC Mg-Li based alloys can be understood with this approach. From the results of the EBSD analysis, it is clarified that the high strength of this alloy is attributed to the combination of Hall-Petch relationship and Bailey-Hirsch relationship.